OF CONCHOLOGY. 209 



ON A NEW CALIFORNIAN TERRESTRIAL MOLLUSC. 

 BY J. G. COOPER, M. D. 



AMMONITELLA, n. g. 



G-en. char. — Testa Ammonitiformis, parva, spira concava, mul- 

 tivolvi, anfractibus lente* crescentibus, verticaliter appressis, 

 ultimo dimidium prsecedentis amplectente ; peristomate simplici, 

 cresentiformi, labro intus parum incrassato ; regione umbilicali 

 expanso, spirse depressions parum profundiore. Animal adhuc 

 ignotum. 



A. Yatesii, Cooper, n. sp. Plate 18, fig. 1-14. 



Sp. char. — A. testa corned glabra, translucente, lineis incre- 

 menti minutis, suturis impressis. anfr. VI et dim. ; depressione 

 spirse crateriformi, tertiam partem lat. testae subsequante ; 

 anfr. ult. supra conice subcompresso, infra rotundato, prope 

 finem declivo et paulo tumidiore ; peristomate verticaliter an- 

 gusto, labro obtuse" incrassato, pariete callosi tateni ; tenui ; 

 umbil. magno, infundibuliformi, anfr. V et dim. monstrante. 



Alt. 0-14, lat. maj. 0-31, lat. min. 0-29, alt. apert. 044, lat. 

 apert. 0*06, lat. spirse 0*10, lat. umbil. 0*10, lat. anfr. ult. 0*08, 

 dep. spirse 0-08, dep. umbil. 0-12, unc. Angl-partibus. 



Gren. char. — Shell like a small Ammonite, the spire concavelv 

 depressed, many-whorled, the whorls slowly increasing in width, 

 vertically appressed, the last half including the preceding, 

 mouth simple, crescent-shaped, the lips a little thickened within ; 

 umbilical region expanded, a little deeper than the depression 

 of the spire. Animal as yet unknown. 



Sp. char. — Shell corneous, glabrous, translucent, with minute 

 lines of growth, sutures impressed ; whorls six and a half, the 

 depression of the spire bowl-shaped, about equal in width to a 

 third of the shell's breadth ; last whorl above a little compressed 

 conically ; beneath rounded, toward the end descending and a 



