Cerion arubanum H.B. Baker, 1924

Original Description

"Cerion uva arubanum, new subspecies

Cerion uva Smith (1898; Proc. Mal. Soc., III, 114); the first Aruba record; collected by Hartert.

Type locality: (A2c) Baranca Alto, Aruba.

Distribution: Aruba; living shells only found in a colony at the type locality and in another just north of Perkietenboseh (A2c, A5a); sub fossil throughout the limestone portions of the island. Similar in habits to uva. 322 adults collected.

Although considerable individual variation (Plate XX) occurs, the last whorl near the aperture tends to jut out tan­gentially in this subspecies, so that the palatal wall of the peristome usually projects out from the preceding whorls to a greater extent than in C.uva uva and knipensis. As a result of this, the umbilicus is usually larger and more open in the specimens from Aruba. In making the measurements of the major diameter in the two subspecies from Curaçao, the calipers seldom touched the aperture, while in C. uva aru­banum, the palatal wall almost always interfered. In all cases, the major diameter was taken exclusive of the aperture, so the true greatest width of C. uva arubanum is slightly larger than the data in Table XIV would indicate. In other par­ticulars, this form is similar to the smaller and more slender lots of O. uva uva, although the whorls tend to be slightly lower than in, any of the Curaçao lots except those from station C13.

The peculiar restriction of the living cerions on Aruba to two isolated colonies is very puzzling, especially since this species very evidently was almost universally distributed on the island in former times. Subfossil shells occur almost everywhere on the limestone, and also are cemented into blocks of phosphate near Culebra (A1). It does not seem possible that this former distribution has been reduced by the extensive cultivation of aloes, as living shells actually occur on this plant in station A4c, while they are absent from the large, limestone plateaus east of Savaneta and Sint Nicolaas, and these hills appear to be mainly undisturbed by man. Although Aruba has a more arid climate than the other islands and appears to be more subject to pronounced dry periods, it is rather diffi­cult to understand how such a resistant species as Cerion uva could have been partially exterminated by these factors. In addition, the living colonies are not in the most heavily wooded places.

                The specimens from the two colonies differ slightly from each other in dimensions, and one lot is lighter in color than the other. However, these divergences hardly seem worthy of rank as separate forms. Some specimens show a slight approach towards C. uva desculptum." (H. B. Baker, 1924:104-105)

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