274 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



CYLICHNID^. 



Genus CYLICHNA, Loven. 



Synon.— Cylichna, Loven (1846), Iud. Moll. Scand., 10.— A. Adams (1850), iu Sowerby's Thes., XI, 558 — 

 H. aDd A. Adams (1854), Genera Keeent Moll., II, 9.— Chenu (1859), Man. Conch., I, 

 385.— Gabb (1864), Paloeont, California, I, 143.— Stoliczka (1863), Paloeont. Indica, II, 

 428— Gould and Binney (1870), Invert. Mass. (2d ed.), 220.— Tryon (1873), Am. Marine 

 Conch., 102. 



Bullina, Eisso (1826), Hyst., IV, 50 (not Ferussac, J821). 



Cylindretla, Swainson (1840), Malac, 155 and 326 (not Pfeiffer, 1810). 



Foharia, Brown (1827), 111. Conch., tab. 39 (uot Lam., 1801). 



'? Mnestia, H. and A. Adams (1854), Genera Keceut Moll., II, 10 (as a subgenus under Cylichna). — 

 Chenu (18r9),Man. Conch., II, 388. 



Etym. — kvXi%vti, a small cup. 

 Type. — Bulla cylindracea, Penn. 



Shell cylindrical or subovate, involute, solid ; spire none, or very rarely 

 a little exposed in the deep umbilicoid cavity of the summit; aperture narrow 

 and ecpialing the greatest length of the shell, rarely produced, and angular 

 above and below; inner lip a little thickened, and bearing a single anterior 

 fold; outer lip simple; surface generally transversely striated, or sometimes 

 puncto-striate. 



The shells of this jjenus resemble .those of Bulla, but are less ventricose, 

 have a narrower aperture, and a fold on the columella. There are also differ- 

 ences in the animal that cause some high authorities to place Cylichna in a 

 distinct family ; while others only separate in a different subfamily, or even 

 merely as a marked genus of the Bullidce. 



Messrs. H. and A. Adams propose a subgenus Mnestia, to include a few 

 peculiar forms that they range under Cylichna. Possibly, these might be 

 better separated generically, though the foregoing diagnosis of Cylichna has 

 been drawn up so as to include both types. Adopting this view, the two 

 subordinate groups may be distinguished as follows : 



1. cylichna, Loven (typical). 



Shell cylindrical, or narrow-subovate ; spire completely wanting, 

 its position being occupied by an umbilicoid cavity ; aperture not pro- 

 duced and angular above or below. — (Type as already stated.) 



2. mnestia, II. and A. Adams. 



Shell with spire visible, sunken in the umbilicoid cavity of the 

 summit; aperture produced and angular above and below; surface 

 marked with transverse bands of color. — (C marmorata and C bizona, 

 A. Adams.) 



