I I.I II;K\M IIIATA. 



lit. 



the anterior basal margin. Surface i umitli in tlit> youn^ and middle stage* 



but with age one or more very s fro i -inal imbrications are developed. In 



aged examples the anterior end i- proportionally narrower than in younger ones. 

 Hinge plate of moderate length with a narrow ligamentul area. Cardinal teeth 

 three in eurh valve, sub-liori/ontal, their inner ends thickene<l and curved down 

 ward. Posterior teeth two in the left and three in the right valve. Both muscular 

 impression- faint. Shell rather thin. 



All the Kentucky types of this species retain the shell and in the absence of 

 unquestionable casts of the interior for comparison with the Minnesota specimens 

 provisionally referred here, there may well he some doubt regarding the actual ex- 



M of the -penes within the borders of the state. The cast represented by fig. 

 30 exhibits certain peculiarities that it seems scarcely likely would occur in casts of 

 the Kentucky form. Thus the outline is less concave in front of the umbones and 

 the length of the shell less than it ought to be in a specimen of this size. The 

 original of tit'iire i->. which i- from the Trenton limestone at Cannon Falls, also 

 di tiers a little, "but in this case oblique pressure has produced distortion that may 

 account for the differences. 



Thisrspeeic* ieetesely related to both f '. Awromr/mrand rnnadensis which Hillings 

 dwuibcd from the lower Trenton or Hlack Hirer limestone of Lmke Huron. Com- 

 pared with iwthontio specimens the first proves to he narrower posteriorly and the 

 seond wider in front, rn the latter the -nmbone are also more inflated. The 

 hinges of the two apacioo ao figured by HiHinps re atoo somewhat 



formation and locality \*n (if the pccle were found In tb.- Ittnlwye nd low.-r Tn-iit.ni 



llmestooe near Hlj;h Hn utky. The uritdnal of Fi*tirv :> i- fn.tu Hi-- tui.ld!.- thirtl of tin- Tfiiton 



balwatSt. Anthony I'ark, Si. I'aul. That of Figure 45 from th. Tr.-nton llmedtooe at Cannon Fall*. 



. TODONTA JANESVILLKNSI8, H. Sp. 

 PLATE XXXIX. riOS. nd . 



Coinp. Cgrtodonta AUKMMNJU BtllingB, 1858, Can. Nat. and Goo!., vol. til. p. 432. 



Shell of medium si/.e, strongly convex, somewhat obliquely ovate, wide-t 

 posteriorly, the hight ami length about as two is to three. Outline almost 

 uniformly rounded for an oval, with a -liu'lit prominence at the beaks and occasion- 

 ally at the posterior end of the hinge line. Anterior end very short. Beaks a little 

 compressed, rather small, incurved, projecting hut little above the hinge. In casts 

 of the interior the umbonal ridge is strongly and the surface in front of it slightly 

 depressed. Anterior adductor scar, well defined, ovate, small, not more than half 

 the size of the posterior scar. The latter as usual is scarcely -liable. 



I'.illial line well in. irk- I. particularly in the basal and anterior parts, llm^e plate 



