CAMBR0-8ILURIAN MICRO-PAL.EONTOLOGY. 55 



When I first found specimens of this type and compared them with 

 Hall and Whitfield's description and figures of their Beyrichia quadrill- 

 rata, 1 was struck by the differences here mentioned, and, naturally 

 enough, believed I had found, if not a distinct species, at any rate a 

 well-marked variety. Since then I have succeeded in collecting no less 

 than fifty species of Ostracoda from the Hudson Eiver or Cincinnati 

 group, and still my collection is without an example of B. quadrilirata 

 as originally figured and described. It would be strange indeed if, after 

 all my search, this species should have been overlooked. Such an 

 event, though possible, is not at all pj-obable. I am, therefore, reluc- 

 tantly obliged to believe that the discrepancies between the original 

 figures and the specimens identified by collectors of Hudson Eiver 

 group fossils with B. quadrilirata, are really the result of imperfect 

 observation. I would be very diffident about making this charge 

 were I not able to prove inaccuracies in their figures of the much 

 better known species B. oculifera, Hall, and B. Chamhersi, Miller. 



This species is one of the most abundant of the Ostracoda of the 

 upper beds of the Hudson Eiver group, and it occurs at many localities 

 in Ohio and Indiana. I have collected it also at High Bridge, Ky., 

 where it occurs in the Birdseye limestone, and from the Trenton shales 

 at Minneapolis, Minn. The specimens from these lower horizons are 

 almost identical with fig. 12, the modifications being too trivial to 

 merit recognition here. 



Figure 13, plate IX., represents a variety from Stony Mountain, 

 Manitoba, that may be designated as var. simplex. It difi'ers from the 

 typical form in having the posteromedian ridge simple instead of 

 bifurcated below. The vertical plates which divide the anterior edge 

 of the typical form into shallow cavities seem also not to have been 

 developed except to a very limited extent. A very similar variety 

 occurs in the Trenton shales of Minnesota. 



In placing this and the following species in the genus Strepula of 

 Jones and Holl, I follow the suggestion of Prof. Jones. While I agree 

 with him in regarding this as the best arrangement possible at the 

 present time, it is well to remark that there is something peculiarly 

 distinctive about S. concentrica and S. irregularis, the typical species 

 of the genus, that does not pertain to either S. quadrilirata or >Si. 

 lunatifera. 



November, 1889. 3 



