LAMELLIBRANCHIATA. 511 
Modiolopsis excellens ] 
strongly elevated filling of the anterior adductor scar. The latter is large, of oval 
shape, horizontally marked in its upper half; sharply defined all around and, because 
of the brevity of the anterior end, is situated partly beneath the point of the beak. 
Posterior scar large, but so faintly impressed that its exact shape cannot be deter- 
mined with the material at hand. Pallial line distinct only in the anterior half, 
where it consists of an obscurely pustulose raised line. 
To 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 end is a little longer than is normal for the species. There is, how- 
ever, no reason to doubt that M. concentrica occurs in Fillmore county, and it is to 
draw attention to its probable occurrence in Minnesota that the species has been 
included in the report. 
Formation and locality.—A common species in the upper beds of the Cincinnati group at numerous 
localities in Ohio, Indiana and Kentucky. Probably also in the Hudson River shales near Spring Valley, 
Minnesota. 
MoDIOLOPSIS EXCELLENS, 2. Sp. 
PLATE XXXVI, FIGS. 13-14. 
This species, of which we have five specimens, is closely related-to—AW. concentrica 
Hall and Whitfield, and was at first confounded with it. A careful comparison 
however proved its distinctness in the following respects: It attains a larger size, 
the casts are more uniformly convex, with the mesial sulcus, 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 
beak 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 JZ. concen- 
trica, Finally, the concentric surface markings are finer and the difference between 
them as developed on the cardinal slopes and on the sides of the shell is a much 
less striking feature. The number of the concentric lines at a point about midway 
between the beaks and the posterior extremity varies in different specimens from 
six to nine in 5 mm. 
What I regard as a nearer ally occurs at the top of the Cincinnati hills. The 
outline of this species is intermediate between figures 6 and 15 of plate xxxvi. In 
its characters also it approaches one almost as nearly as the other. 
Formation and locality.—Upper part of the Hudson River group, Spring Valley and Granger, 
Minnesota. 
Mus. Reg. No. 8374. 
