262 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



its lingual membrane (PI. V. Fig. Q) long and narrow ; teeth 24 — 1 — 24, with 

 6 perfect laterals. Centrals with the base of attachment longer than wide, with 

 expanding lower lateral angles, and squarely reflected upper margin ; reflection 

 large, stout, bearing small but distinct side cusps, with short, blunt cutting 

 points, and a long, stout median cusp reaching the lower edge of the base of 

 attachment, beyond which projects the long, acute cutting point. Laterals like 

 the centrals, but asymmetrical by the suppression of the inner, lower, lateral 

 angle of the base of attachment, and the distinct inner side cusp and cutting 

 point. Marginals subquadrate (b), a simple modification of the laterals, the re- 

 flection being more developed, and bearing one inner, oblique, long, blunt cut- 

 ting point, and one smaller side cutting point ; the extreme marginals (c) are 

 rather wider than high, and the cutting points are bluntly rounded. 



Fig. 155. 



Gonostoma Yate3i, J. G. Cooper. 



Shell globosely planulate, equally depressed above and below, widely umbil- 

 icated, thick, smooth, scarcely marked with incremental stria?, horn-colored ; 

 spire sunken, apex obtuse ; whorls Qh, slightly convex, each 

 one raised above the preceding one, the last tumid, obsoletely 

 carinated, descending at the aperture ; aperture, oblique, lat- 

 eral ; peristome thickened, white, its extremities far removed, 

 scarcely reflected, above deflected and sinuous ; umbilicus very 

 wide, showing all the whorls. Greater diameter 9, lesser 7 

 mill. ; height, 4 mill. 



Ammonitdla Yatesii, J. G. Cooper, Am. Journ. Conch., IV. 

 209, PI. XVIII. Fig. 1-14, figure reversed (1869). 



G. Yatesi. 



In the California Region, in Calaveras County, California, 

 at Cave City. 



Jaw and lingual membrane: see above p. 261 (PI. V. Fig. Q). 

 Genitalia unobserved. 



POLYGYRA, Say. 



Animal heliciform ; mantle posterior ; other characters as in Patula. 



Shell umbilicated or perforated, orbicularly flattened, obliquely and costu- 

 lately striate ; whorls 5- 7^, gradually increasing, the last anteriorly constricted, 

 briefly deflected, inflated below, devious, the penultimate 

 whorl plainly conspicuous, very often constricting the 

 rimate umbilicus; aperture subreniform, or irregularly 

 sinuate ; peristome narrowly reflected, heavy, its mar- 

 gins usually dentate and joined by a triangular, denti- 

 form callus, obliquely entering on the parietal wall of the aperture. 



Interior and Southern Region, especially the latter in North America. It 

 is also represented in the West Indian Islands, in Mexico and Yucatan, and 

 one species is found in Bolivia. 



Fig. 15G. 



Animal of P. septemvolva. 



