1. \MKU.1I.K\M Ml \ .Ml 



lMl 



-frongly elevated tilling of tin- anterior adductor scar. Tin- l.ittor is large. <>f oval 

 shape. hori/.ontally marked in it- upper half, sharply .lelined all around ami. became 

 of tin- brevity of the anterior end. is -it nated partly I.eneath the point ot' tlje l*ak. 



> faintly impressed that its exact shape cannot U> deter- 



mined with tin- material at hand. 1'allial line distinct only in the anterior half. 

 where it con>i-ts of an obscurely pii-tulose raised line. 



'I'o this species I refer provisionally a badly distorted mould of the exterior of a 

 right valve, collected by me at Spring Valley in 1887. Its surface is marked 

 precisely as described above, but the reference is still rendered doubtful by the fact 

 that its anterior eii'l i- a little longer than is normal for the species. There is, how- 

 MO reason to don I >t flu* M. >nr>-nlri<-<i occurs in Fillmore county, and it is to 

 Iraw attention to its probable occurrence in Minnesota that the species has been 

 included in the report. 



ility.- A iviiiiiiiiiii S|V.TU-S in th- u|>j.r IM|- ,,f it,.- Cincinnati k'r"iip at 

 ;- in Ohio, Indiana and Ki-nturky. I'mliably also In tin- Ilinl-m Ki\.-r shall", rn-ar Spring Valli-y, 

 Mlnncsot*. 



MoDIOLOPSIS KXCELLKMS, M. 8f. 

 PLATE XXXVI ^ li. l-|4. 



This specie^, of which we have tive specimens, is closely related to M. concentric,! 

 Mall ami \\ hitfield. and was at first confounded with it. A careful comparison 

 howevi-r proved its ili>t inertness in the following respects: It attains a larger size, 

 the casts are more uniformly convex, with the mesial snlcus, on both the shell and 

 the cast, much shallower, for which reason the ventral margin is very slightly 

 convex where it is sinuate in that species. The outline differs also in the postero- 

 cardinal region being less uniformly curved and more prominent at the extremity 

 of the hinge. The anterior end is longer so that a line drawn from the point of the 

 1'cak across the shell at right angles to the hinge line passes within the inner border 

 of the anterior adductor scar, whereas it cuts a third of the scar away in M. mncen- 

 Finally, the concentric surface markings are liner ami the difference between 

 tin-in a developed on the cardinal slopes and on the sides of the shell is a much 



-triking feature. The number of the concentric lines at a point about midway 

 -seen the beaks and the posterior extremity varies in different specimens from 



to nine in < mm. 



What I regard as a nearer ally occurs at the top of the Cincinnati hills. Tin- 

 outline of this species i> intermediate between figures ti and ]:\ of plate .\.\.\\i. In 

 its characters also it approaches one almost as nearly as the other. 



nation and /.- Pt>cr part of the Hudson Kiv.-r K"-up. Sprint; Valley ami Granger, 



Iflooeaota. 



W M /.. ; N - .:; 



