ODONTOSTOMUS. 



97 



This species differs from 0. dentatus in the quite vertical aperture, 

 the oblique, not subvertical, direction of the columellar lamella, the 

 straight, instead of abruptly bent, upper palatal fold, and generally 

 less developed dentition of the aperture. The transverse plate 

 behind the lower palatal fold in 0. dentatus is generally wanting in 

 patagonicus, and the total number of teeth is normally 3 or 4, rarely 

 7 or 8. The ordinary size is 20-23 mill, long, though it may attain 

 27 mill, long, 12 wide. Dr. A. Doering, from whose account these 

 details are taken, figures two specimens, the largest of which I have 

 reproduced (fig. 22). 



O. ROCAE (Doering). PI. 14, figs. 18, 19. 



Shell rimate, ovate-oblong, rather solid, brown, opaque, slightly 

 shining ; ornamented with close, nearly regular striae ; spire ovate- 

 subcylindrical, the apex conic, suture impressed. Whorls 8, a trifle 

 convex, the first two nearly smooth, buff-corneous, the rest brown, 

 regularly sculptured with close, almost rib-like stride, sometimes 

 whitish ; the last whorl about one-third the total length, chalky- 

 white around the aperture. Aperture subvertical, ovate, calcareous, 

 nearly closed by 8-10 folds, of which three are stout and lamelli- 

 form : one angular, twisted and grooved parietal lamella, the second 

 and largest tongue-shaped, on the columella, the third twisted, 

 within the middle of the right margin ; besides which there are 3 to 

 5 minute parallel folds within the basal lip, two small ones within 

 the upper part of the outer lip, and a strong transverse lamella deep 

 within the mouth. Peristome expanded, labiate, the margins joined 

 by a callus. Length 21-24, diam. 8-9, length of aperture 7-9, 

 width 61-74 mill. (Doer.}. 



Argentina : Southern slope of the Sierra de Otirrumalan, in damp, 

 shady places. 



Plagiodontes rocae DOERING, Informe Oficial, etc., de la Exped. 

 al Kio Negro, Entr. i, Zoologia, p. 65, pi. i, f. 5, 6 (1881). 



Distinguished from its allies by the dark color, becoming white 

 near and in the aperture, the rib-striaa, etc. The locality is near the 

 Sierra Ventana. 



O. D^DALEUS (Deshayes). PI. 14, figs. 1-9. 



Shell perforate and rimate, ovate, swollen, whitish, finely and 

 densely striate. Spire conic. Whorls 6^-7, rapidly increasing, the 



