244 THE CHICAGO ACADEMY OF SCIENCES. 



aperture roundly and regularly elliptical, continuous in many specimens, 

 a trifle effusive at the lower end; outer lip thin, sometimes developing 

 a white deposit or varix a short distance from the edge; inner lip 

 markedly and broadly reflected over the umbilicus, forming a broad, 

 even expansion; parietal callus well marked, thick; umbilical chink 

 well marked, open, axis straight, not twisted, thickened by shelly de- 

 posit. 



Length. Breadth. Aperture length. Breadth. 



4.50 2.50 1.50 .50 mill. Type parva 



7.75 4.10 3.50 1.50 " Type curta 



6.00 3.00 2.50 1.25 " Allegheny Co., Penn. 



5.00 2.75 2.25 1.50 " Dyer, Indiana 



9.00 4.50 3.80 2.00 " Des Moines, Iowa 



8.00 4.00 3.80 1.90 " 



7.50 4.00 3.50 1.75 " 



7.25 3.75 3.00 1.50 " 



6.25 3.10 2.90 1.50 " 



TYPES : Smithsonian Institution ; parva, fourteen specimens ; No. 

 119418, all immature; curia, four specimens, No. 118632; tazewelliana, 

 location unknown. 



TYPE LOCALITY : Parva and curta, Cincinnati, Ohio ; tazevvelliana, 

 Tazewell shore, Illinois River, Illinois. 



ANIMAL : Color blackish, very thickly dotted with fine white dots. 

 The upper whorls are pinkish in the living animal, and the spotted 

 mantle shows through the almost transparent shell. A specimen with 

 head and foot protruded, measured as follows : 



Length of foot and head. Width of foot. Length of shell. 



4.25 2.00 7.00 mill 



JAW : Superior jaw a trifle more than three times as wide as high, 

 not notably arched, with a small median swelling on the ventral margin ; 

 the jaw resembles that of umbilicata. 



RADULA : Formula : JJ+f +J+|+}+f +}( 24-1-24) ; central tooth 

 with a rather long cusp; lateral teeth tricuspid, very wide, the small 

 entocone forming by a splitting of the large mesocone ; ectocone rather 

 large; the marginal teeth commence at the seventh tooth, in which 

 the entocone and mesocone are about equal in size and appear at the 

 distal end of the reflection; the typical marginal teeth begin with the 

 tenth tooth, the distal end of the reflection becoming serrated, while 

 the outer edge develops several small serrations. The marginal teeth 

 are long and narrow, and there is considerable variation in the number 

 and position of the individual cusps. Eighty-two to ninety-five rows 

 of teeth were counted. The general form of the teeth are not different 

 from those of umbilicata (pi. VIII, fig. A). 



