Strophia nivia Maynard, 1894
"STROPHIA CURTISII NIVEA Novo.
SP. CH. Size, medium. Shell, not very heavy. Striations,
present. Teeth, two, and both small. Whirls, ten. Examined forty
Form of shell, a pointed cylinder, with the first whirl the largest,
then the next three are successively a little smaller, after which the
shell slopes rather gradually to a point, forming an angle of 45 degrees. The striations are not numerous, twenty-two on the first whirl, are not prominent, are irregular in form, and not arranged in lines; they are narrow, being about one half as wide as the interspaces between them; are smooth and rounded.
Aperture, rather small, and slightly contracted at the entrance. Lower tooth, very short, about .02 high, and about three times as long as high. It is about central in position, and is set well back from the frontal bar, about .08. The upper tooth is also set well back, and is about as large as the lower.
Margin, produced forward nearly as far as the diameter of the shell, and is inclined very slightly to the right, the edge is very thin, about .02, and is produccd upward into a sharp edge, but not rolled backward. The frontal bar is not very prominent, and the striations ppear within it. Color, externally, pure white without fleckings; within the aperture, slightly tinted with flesh color.
Size of type, .90 by .37. Largest specimen, I.06 by 47. Smallest,
.82 by .38. Greatest diameter,.47 ; smallest, .35. Longest specimen,
1.06; shortest, .87
Variations are chiefly in color.
No. 1. Pure, snowy white without tinting of any kind, within or
without. Striations even smaller than in the type and fewer; a single
specimen of this beautiful form was obtained.
No.2. Flecked slightly with pale reddish, and with more
numerous and more prominent striations. Shell, thicker and heavier,
with a thickened margin.
From this flecked form specimens grade, but through a very
small percentage, into typical S. curtissii, hence I have not given
the form full specific rank, as it is an example of an incipient species which has not become fully fixed. Known from all other Strophias by the short, central tooth and peculiar snowy whiteness.
DISTRIBUTION AND HABITS
I found the Snowy Strophia clinging to the trunk and limbs of
the banyan tree which stands near the old ruin in the cemetery, where Strophia curtissii is found. The back of the banyan is nearly white and the shell has assumed a protective color, and, as in most cases where a light form of Strophia has become evolved from a dark form, the shell has become thinner, thus reducing the size of the striations snd margin of the aperture. This lightening of the shell must prove beneficial to the animal in living on trees, but in spite of this, we find that in order to assist the animal to maintain control over its shell the upper tooth has not only beoome more prominent, but the aperture is contracted and its margin is extended forward.
No one can doubt the originator of this form of Strophia, as it is now easy to trace it back to its ancestor, and the lesson that it teaches us is of great importance in our studies of land shells, more especially of this genus. Strophia curtissii is a speeies which lives very near the ground, in fact, is frequently found on the ground, hence is liable to injury from many causes. Here we find the animal protected by a moderately heavy shell, flecked to resemble the mottled bark of trees and parti-colored herbage on which it lives. Some offspring of this mottled form ascends a white-barked tree, where they are no longer in danger of being crushed by the feet of passing animals, but are exposed to another class of dangers. Hence gradually through successive generations the animal secretes a shell better suited to its new method of life. First, it loses its color, then the shell grows thinner and lighter, but in order that the animal may grasp it more firmly and prevent its being blown away during the prevalent tempests which occur, when the Strophia must be actively moving about, in August and September, for there is considerable rainfall in both these months and mollusks of this genus move in damp weather, a tooth is developed, which is not usually found in the ancestor, S. curtissii, namely the upper, and the aperture is narrowed and its margin pushed forward. These are apparently slight alterations, but they mean much to this small animal, and are as comparatively important to it as more easily seen changes in other and larger animals. We have seen how the form of Strophia curtissii living on Spotter's Key has altered its shell to suit its new home. Now who can say but what the animal within the shell has not changed also. At all events, an important portion of the animal has changed. Now, when I maintain that such changes after becoming fixed, as in time they do become fixed, as we find they do in many cases in this genus, constitute good and sufficient specific characters, I may be indulging in the rankest kind of conchological heresy; but is not such heresy, when, guided by facts, I apply the truths of evolution, in which every thinking naturalist believes, practically, in the naming of species, better, as indicating progression in the right direction, than conservatism, which means stagnation? I simply trace the changes which those :animal are undergoing and, believing as I do, that all animals have halting places in the great system of changes, I endeavor to indicate these halting places by imposing a name upon the animal, which, assuming certain characters, has become quiescent as a form, for a time.
I once again repeat, what I have had occasion to state many times, and be it remarked I speak from a long and extended experience, that the genus Strophia is exceedingly plastic, evolving species much more readily than many genera of shells. The species are exceedingly local in distribution, and slight causes isolate colonies, that when so isolated speedily assume characters consistent with their environment, and these characters I consider, as I am forced to do, looking at the whole matter broadly and consistently, as specific. In my account of the genus Strophia I have been very careful not to overstate anything, nor have I formed any theories unsupported by facts, and as far as I have gone I nave not taken any steps which I wish to retrace.
I feel constrained to make these and similar remarks, inasmuch as I know that I am looking upon the matter which I have in hand, from a new and a widely different standpoint from which it has been viewed in the past. The correctness of my judgment may be, possibly justly, questioned, but I do trust no one will venture to pass an unfavorable verdict whe he has not been over the ground as completely as I have been
over it, exploring those far away and often nearly desolate keys almost yard by yard, noting, and carefully recording, every attendant circumstance and surrounding that can possibly have any bearing upon the lives of these interesting mollusks. I care not what experience one has had with other genera of shells, for while it is true that this may assist him in many ways, it does not fit him to pass positive judgment upon the work of one who has; had an extended experience in a genus of shells so
peculiar as is Strophia. For be it remembered, it is a portion of my heresy to believe that we cannot always form cut and dried rules that will apply to all groups of anyone class of animals, even though these groups be closely allied.
For an example, while we might, with perfect propriety, think a man very unscientific who would maintain that color variation, or the weight of the shell of the common Purpura lapillus, of our coast, were of the slightest specific importance, yet both of these characters (color and weight) are of vast importance, as I have repeatedly shown, in Strophia. Color, in a species of Helix (H. varia) which often grows side by side with species of Strophia, counts for nothmg, specifically, as we find all gradations in, this shell from pure white through a beautiful banded form to nearly black, nor is the weight of the shell of any great importance (although it may be somewhat so) in this species, nor is it, I believe, in any members of this genus. Why
color should be important and protective in one group, and not in another, is difficult to say, bnt so it is. Nearly black specimens of the Varying Helix may be found side by side with white examples. Weight of shell means more with Strophia than with Helix as one animal (Helix) has a muscular attachment and the other (Strophia) has not; thus members of the genus Strophia, with a changed weight of shell, naturally are obliged to assume other vital characters which need
not be assumed by a Helix when it changes the weight of its shell. Hence one may be well posted in regard to all the changing ways and characters of even so closely an allied genus as Helix and yet know very little of the peculiarities of the members of the genus Strophia.
But I think I have now said enough to convince anyone that he ought, at least, to pause before giving an adverse opinion of my statements until he has seen as many of the members of the genus Strophia in their native islands as I have.
I did intend to leave much of the matter that I have given in these somewhat lengthy digressions, until I came to my general conclusions, after going completely through with my monograph, for I have been greatly encouraged by the confidence which many have shown in my work, especially among the rising generation of naturalists, but as I have read, here and there, some occasional allusions to my opinions in which the authors quite evidently judged me upon too general grounds, without looking into the heart of the matter, I thought it best to make these explanations. I now, however, will say that I have done, and shall make no more digressions of this nature until the completion of my work. This I will say, however, before quite ending the subject, should there now remain one doubting Thomas who still thinks that there should be given today no more species of Strophia, for example, than are given by Reeve in his monograph (some twentyfive, I think), and that I have been too expansive in my number of species, I now most cordially invite him to accompany me on my next trip to the Bahamas, which will probably be next spring, or on any following trip, and I will venture to say that I will show him more things in the genus Strophia than he ever dreamed of in his wildest