50 RESEARCHES L'PON THE HYDR0BIIX.5 



Type P. corolla, Stm. — Melanin corolla, Gould, Proc. Bost. Soc. Nat. Hist., 

 II, (1847) 223.— Amnlcola corolla, Gould, U. S. Expl. Exped., Moll., (1852) 

 129, pi. ix, fig. 149, a-c. New Zealand. 



No other species is as yet certainly known to belong to this 

 genus. There are other coronated species belonging to the 

 family which must be placed in it, if they are found to agree 

 with it in the lingual dentition, the peculiarities of which consist 

 in the form of the rhachidian tooth, which is not strongly trilo- 

 bate below as in the other genera of the group, in the approxi- 

 mation of the very small basal denticles of the same tooth to the 

 lateral margins, and in the great number and equal size of the 

 denticles of the intermediate tooth. 



The dentition was made out from the type specimen of Am- 

 nicola corolla, Gould, in which the animal was found uninjured 

 after more than twenty years' desiccation. This specimen is in 

 the museum of the Smithsonian Institution 



COCHI.IOPA,' Stm. 

 Cochliopa, Stimpson, Am. Journ. of Conch., I, (1865) 52. 



Shell depressed-conic ; base concave, carinated ; umbilicus large 

 and deep ; aperture oblique. Operculum thin, corneous, sub- 

 spiral. Rostrum of moderate size; tentacles rather long, taper- 

 ing. Yerge rather elongated, compressed, geniculated, and bifid, 

 the inner branch being very small, less than one-fourth the size 

 of the outer one and arising at the inner angle of the geniculation. 



Lingual dentition of the typical species : Rhachidian tooth 

 short and broad; middle lobe of the basal margin very broad ; 

 basal denticles rather large. Intermediate tooth wnth a long pe- 

 duncle, and square 1)ody having a cavity in the centre. Lateral 

 teeth with an expansion of the inner side of the shank, separated 

 from the summit by a deep rounded sinus ; the outer lateral 

 being more expanded than the inner. Formula of the denticles : 

 ^-8-18-24. 



Station, fresli water. 



Distribution, California. 



Type C. liou-ellli, Stm. — Amnicola Rowellii, Tryox, Proc. Acad. Nat. Sei. 

 Phila., 1863, p. 147, pi. i, fig. 8, 9. — Head black ; tentacles yellowish, with 



' Ko^xl;, cochlea parva ; 'tth, foramen. 



