Brasilennea arethusae Maury, 1935

Original Description

"Brasilennea arethusae, sp. nov.

Figs. 1,2 and 4: Holotype, Amer. Mus. No. 24237.

Fig. 3: Cotype, Amer. Mus. No. 24238.

Fig. 5: Cotype, Amer. Mus. No. 24239.

Shell of medium size, the adult form convexly subcylindrical with the greatest breadth near or a little above the center of the shell.  Volutions many, with their sides convexly flattened. Sutures linear and distinct.  Apex of the shell obtusely pointed, but only very slightly elevated. The first two-and-a-half to three whorls are smooth, glossy, with their sides gently convex. Thereafter the subsequent whorls become more and more strongly sculptured with very fine, narrow, closely-set, sharply-defined ribs, which on the center of the shell number nearly three to a space of one millimeter. There is a graceful change in the direction of the trend of the ribbing, the ribs on the spire being very oblique, but those on the last volution are almost vertical. In the adult shell the last whorl narrows markedly, and on the aboral side shows two strong external sulci, one central, the other basal and defining the conspicuous perforation of the shell. Aperture with two pronounced folds within. One fold is on the columella, well shown on one specimen to be strong and rounded, while the other fold is sharper and is on the upper inner margin of the aperture, nearly median. Outer lip straight, with a parallel lamella on a perfect shell. Height of adult shell 25 mm., greatest width14 mm.; height of aperture measured obliquely,9 mm., greatest width of aperture 7 mm.

In addition to the adult shells, there are several young shells proved by their sculpture and form of the upper portion to be adolescent members of this species, although they are strikingly unlike the adult shells in form. The young shells are subdiscoidal, widest at the base, the last

whorl having the greatest diameter. The first two or three volutions are smooth, while the upper surface of the following volutions bears fine, oblique costae. On the body whorl of the adolescent shells the costae terminate suddenly at the sharply angulate periphery of the whorl, the under surface being smooth except for microscopic growth lines. The aperture is angulated by the sharp periphery, and the perforation is deep. One young shell measures 4 mm. in height and 7 mm. in greatest diameter; another is 6 X 9 and includes about seven whorls.

This species is dedicated to the sylvan nymph, Arethusa, in reference to the terrestrial habits of this very interesting Brazilian mollusk.

LOCALITY. - Fazenda São José, Municipality of Itaborahy, State of Rio de Janeiro, Brazil, In a pure, light-yellow limestone.

HORIZON - Probably Miocene, but possibly as young as Pliocene."   (Maury, 1935:4-6)

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