O8TRA>l>\ 



t I 



\\\ i ii", rron < 



PI. A 1 PIOB. 



n.: hltfht 7.') ID in : ihii-knt-s o 4* mm. A larjror S|M-IIII. ii hata li-rik'th of 

 about I :> nun. 



Tlii- is an uini-nally short, subovate form, the ends being nearly equal ami, with 

 the dorsal margin, forming an almost regular elliptic curve; ventral outline straight, 

 centrally; surface smooth; valves moderately and uniformly convex, one larger ami 

 strongly overlapping the other above. l,elo\v and at one end. The end having no 

 overlap is slightly narrower than the other. 



The suhequality of the ends, especially as regards thickness, makes it difficult 

 if not impossible to determine with certainty which is the right and which the 

 left valve. Asa Bytkoqjprittiu larger of the two must be on the left side, and if this is 

 correct for the species, then the blunter of the two ends would be the anterior. ID 

 ////;/>, a genus containing mostly elongate species, the right valve overlaps, but 

 the carapace in the present species is too short for that genus. Of known species Ii. 

 .lone- ami lloll.a Wenlock form originally described as a variety of CytliercUimi 

 * may be nearest, but differs like all other species of Hythocypris in being 

 longer. 



Formation and locality.- Middle third (Rhinidictya bed) of th<- Treotoa shall*, St. Paul, Minnesota. 



BYTHOCYH NTI, n. sp. 



PLATK. XI. IV. F108. 



L<Ti>;th 1.40mm.; night 0.68 nun.: thickness 0.7 nun. 

 Length I 17 nun.: bight 0.57 mm.: thlcknetut 0.6 mm. 



Valves strongly convex, especially so ventrally, somewhat elongate elliptical in 

 outline, the ventral margin convex but not so much as the dorsal, the ends sub- 

 equally rounded but with the posterior one a little blunter than the anterior; surface 

 smooth. 



This species is readily dfctingnithed from //. rylin<lri<-n Hall, by its more equal 

 ends and convex basal outline. It seems to be closely related to //. condnna Jones, 

 of the Wenlock shales of England, but the outline is a little different and the valves 

 thicker in the ventral part. The left valves of Knin.-n-lln imequalis and A', arniafa 

 are somewhat -imilar yet not enough so to render confusion between them at all 

 likely. 



The species is named for the promi-ing geologist. l>r. Ulysses S. (Sraut. of the 

 Geological Survey of Minnesota. 



Format* and locality. Middle third (Rhinidictya bed) of th>- Tr- -nt-.n shales, St. Paul and MINN. - 

 apolls, Minnesota. 



Ann Ms. Xl BbU Mr. 4, rol. III. pi. ztr. If 4, 1MB. 

 -44 



