I.AMKI.I.lHKANi I11AI \ 589 



'.!. I 



and passing gradually into the broadly and uniformly curved posterior r 



basal line most proinii t an. I >tn>n^: \ liehind the center, in frontof which 



point it ascends rather npidly with a much more gentle curve into the short, small 

 ami sharply rounded anterior end. Umbones full, large and prominent, beaks 

 -null ami .trontfly incurved: umliomil ridge siihangular near the beaks only, iucon- 

 -picmui- in a lateral view. Surface marked with concentric lines of growth. These, 

 with the exception of a few near the margin, are obscure in the material at hand. 



Mental area very narrow. Hinge plate of moderate strength, with three slightly 

 curved and nearly horizontal cardinal teeth and two or three slender posterior 

 lateral teeth in each \al\ Pallial line and anterior adductor muscle distinct, the 



! rather small and of obovate or subrirrular shape; posterior adductor faintly 

 impressed, -ituated immediately beneath the lateral teeth. Internal umbonal 

 sulcns and ridge slightly developed but always distinguishable on good casts of the 

 interior. 



Although closely simulating several others this is still to be regarded as a well 

 marked species. It may be compared with C. huronensis Billings but will be found 

 to be higher, more erect and more ventricose. The umbones also are larger and 

 the cardinal teeth longer and more nearly horizontal. C. obliqua Meek and Worthen 

 has a straighter basal line and is more produced in the postero-ventral region. C. 

 ylaMlus and C. persimilis have a more rounded outline and smaller umbones. C. 

 subovata is longer, wider in front, not so ventricose, and has smaller umbones. A shell 

 that is likely to prove more troublesome to separate than any of these is the './/<- 

 iixfinla decipiens. They are associated in the same strata at Minneapolis but when 

 good casts are available they may be distinguished at once by the higher position 

 and much greater sharpness of definition of the anterior muscular scar in the 



I '<inuj-fmi<i. 



It i> i>MiMe that the \Visconsinspeciesreferred by Whitfield to Cypricm 

 ventricosus Hall, sp., in 1882 (loc. cit) is not identical with C. f<illing*i, because lu> 

 illustration, if correctly drawn, would indicate a distinct form. However that may 

 lie it is quite certain that he had this species before him when he drew up his 

 description, since it is not uncommon at the localities mentioned by him. It is 

 en-tain also that neither the specimen figured by him nor the form now narm-d 

 after Mr. K. Hillings, the founder of the genus, are the same as the types of Hall's 

 /;.///,Wm rentrii',,*,! (Pal. N. V.. vol. i. p. I'M: 1M7|. Indeed they are widely di- 

 tim-t <pecies the last having proved to be a true White/la and n<> nor 



'odonta at all. On page 271. Pal. N V . vol. iii. Hall figures another species of 

 t'Hlnntti which he refers to his vtntricoaa as a ral<mr>;i. Th i- w 



same as C. billingsi being longer and having a well developed legamental area and 



