THE NAUTILUS. 99 



lip is arcuate below, straightened above, heavily calloused in adults, 

 especially above, and in contact with the preceding whorl only for a 

 very short distance. There is a somewhat flattened umbilical area 

 below the perforation, closely marked with growth-striae, and 

 bounded by an angle, which is sometimes not very distinct. 



Length 5.3, diara. 4.5, aperture 3.1 mm. 



Length 5, diam. 4.5, aperture 3.1 mm. 



Coy river, on the road to Tampamolon; State of San Luis Potosi. 

 Types no. 99023 A. N. S. P. 



This is the first Somatogyrus from west or southwest of the Mis- 

 sissippi river system. 



COCHLIOPA COMPACTA n. sp. PI. ix, figs. 4, 5. 



The shell is depressed, solid, rimate, pale greenish olive, encircled 

 with few or many dark olive or blackish lines and narrow bands, 

 and sometimes a few cream-white bands. Spire convex, very nar- 

 row when viewed from above. Whorls 3^ to nearly 4, the early 

 ones smooth, the last very wide, rounded, sculptured with low spiral 

 threads or nearly smooth, descending to the aperture. The aperture 

 is rotund-ovate, angular above, the outer lip slightly thickened, 

 columellar and parietal margins thick. The umbilical area behind 

 the columellar lip in fully adult shells is white and wide, the basal 

 rimation either long or rather short. 



Alt. 2, diam. 3.9 mm. 



Choy river at the cave, south of Las Palmas, State of San Luis 

 Potosi, Mexico. 



This species is closely related to C. ptcla, differing by the larger 

 aperture, compressed and generally closed umbilical region, and the 

 peculiar area behind the columellar lip of adult shells. It was taken 

 in considerable quantity. 



The figures represent one of the most common color-forms. Other 

 examples have lines and bands over the base also; and in some these 

 markings are reduced to a few wide bands. 



COCIILIOPA RIOGKANDEN'SIS Pils. & Ferr. 



Valles river at Valles and AVillis's ranch; Ganina river near 

 Rascon. It is an abundant and variable species. In some examples 

 the last whorl becomes free at tiie aperture, reminding one of the 

 small shell described as Valvata micro. That species may prove to 

 be a Cochliopa. 



