688 TEE PALEONTOLOGY OF MINNESOTA. 



[Bylhocyprl) cyllmlrlca. 



of the interior. This internal thickening recalls Cytherellina siliqua Jones, which 

 this species also resembles in its external characters, but the casts of that species 

 are marked with two sulci instead of one. Still, I am not all satisfied that these two 

 forms are not strictly congeneric. The sulcus in the casts of B. cylindrica being just 

 behind the center, it corresponds with the posterior one of the two in the Cytherell- 

 ina. As to the anterior one, would its absence be of any great consequence? While 

 it does not seem to me now that it w6uld be, it is deemed wisest to defer a decision 

 on the point, since the verdict would necessarily involve many others of the paleozoic 

 species now referred to Bythocypris. Of the latter, B. testacella Jones, from the 

 Weulock of England, differs chiefly in being more elongate and less broadly rounded 

 posteriorly. 



In the Canadian publication above cited, I referred a valve from the Hudson 

 River group of Manitoba, to this species. That the identification was incorrect, I 

 am now fully convinced. The figure, which was probably drawn in a reversed 

 position, shows a left valve, agreeing very closely with the Wenlock species B. 

 concinna Jones. Perhaps it should be referred to that species, but it would be well 

 to await the discovery of more conclusive evidence before such a course is finally 

 decided upon. 



It is scarcely necessary to show why B. cylindrica is neither a Primitia nor a 

 Leperditia. As to its identity with Eichwald's Cypridina, later Leperditia minuta, 

 which Prof. Jones refers to Primitia (loc. cit.) and I to the new genus Primitiella, is a 

 question that it seems to me can be answered only in the negative. The minuta, as 

 figured by Prof. Jones from Russian examples of the species, has dorsal angles with 

 a long straight back, giving it on the whole a decided primitian aspect, which 

 certainly is not the case with the true B. cylindrica. In the same paper Prof. Jones 

 figures two Cincinnati specimens, presumably of the latter species, to show their 

 similarity or identity with the Russian P. minuta. He represents them as having a 

 straight hinge and obtuse dorsal angles, the valves being figured, according to my 

 interpretation, in a reversed position. As to these features I can only say that I 

 have never seen any specimen in which they were present; and this can scarcely be 

 because of a lack of material, for, of all the Cincinnati Ostracoda, B. cylindrica is by 

 far the most abundant. Prof. Jones' figures being like Hall's figure of the species, 

 is it not possible that the drawing of the former was biased by an examination of 

 the latter? 



Formation and locality. Rare in the Galena shalrs near Cannon Falls, Minnesota. Very abundant 

 in the lowrr bed-, nf the Cincinnati group, ;it numerous points in the vicinity of Cincinnati, Ohio. Very 

 large si>eeimeiis, 2.0 nun. and more in length, occur in the- upper beds of the same formation. These were 

 referred to the species by I)r. S. A. Miller, but are not taken into account here because they are probably 

 distinct. 



