“690 THE PALEONTOLOGY OF MINNESOTA. 
[Bythocypris? robusta. 
BytHocypris (?) ROBUSTA, ”. Sp. 
Sa 
a, 
Fig. 52.—a, a left valve, with somewhat blunter ends than usual, showing position of subcentral 
spot; b, right side of entire carapace; c and d, ventral and posterior outline views of same; lower Trenton 
(‘‘ Lower Blue limestone”), Dixon, Illinois. 
SizE.—Length 2.5 mm.; hight 1.05 mm.; thickness 0.87 mm. 
Carapace elongate, subelliptical or obscurely triangular, the outline convex 
dorsally and nearly straight or gently arcuate ventrally; anterior end strongly 
rounded and somewhat higher (blunter) than the posterior. In a ventral view the 
outline is wedge-shaped, the higher or anterior end being much more attenuate 
than the other. Valves rather strongly convex, unequal, the left overlapping the 
right all around except at the posterior extremity; dorsal edge of left valve some- 
what thickened; posterior extremity of right (smaller) valve subacute; surface 
smooth; each valve occasionally showing a small discolored spot a short distance in 
front of the center. 
The affinities of this fine species are doubtful. It is not a true Bythocypris, nor 
is it any more like either Macrocypris or Pontocypris. Perhaps it should be placed 
under Bairdia since it resembles certain species that have been referred to that 
genus by Jones and Holl. Yet, after a careful comparison with numerous Devonian 
and Carboniferous species of Bairdia, I have come to doubt the propriety of recog- 
nizing that genus in any of the known Lower Silurian species. The acuminate 
posterior extremity of the right valve reminds as much of the new genus Krausella, 
and it is an alliance with this genus that I would favor more than with Bairdia. 
Specifically, B.? robusta will be distinguished at once from all known Lower 
Silurian Cypride by its large size. 
Formation and locality.- Lower Trenton limestone, Dixon, Illinois, where it was found abundantly 
in association with Krausella inequalis and Schmidtella crassimarginata. 
