Descriptions of new species of Leptcena and Cyclonema. lol 



Descriptions of one new species of Leptcena, and two sp)ecies of Cyclonema 

 from the Lower Silurian Rocks. Cincinnati Group. By U . P. James. 



Leptoena Aspera. — James. 



[Leptaena rugosa.— J a^es. Catalogue of L. Silurian Fossils, 1871.] 

 [Zjepdxna sericea (?)— Meek. Pal., Ohio, 1873.] 



[^Aspera, in reference to roughness.] 



Shell small, transverse ; width nearly twice the length ; hinge line 

 generally about equal to the greatest width of the shell farther forward — 

 in some individuals more — and sharply pointed at the extremities (nearly 

 all of the uninjured specimens taken directly from the clay bed have 

 the extremities of the hinge line thus pointed); lateral margins round- 

 ing quite abruptly to the front. 



Dorsal valve concave, the slope dropping, in most cases, nearly at 

 right angles under the beak and about half the length of the cardinal 

 line, in others the slope is gradual ; beak not projecting ; area narrow, 

 drooping forward ; cardinal line straight,, and having a crenulated ap- 

 pearance, most conspicuous when held to a strong light ; wrinkles 

 commencing at the hinge line and extending inward, obliquely, cross- 

 ing the striae at nearly right angles. 



Ventral valve moderately convex on the umbone ; cardinal line 

 sloping slightly from the beak to the lateral extremities ; beak not in- 

 curved ; cardinal area much the widest in the middle, and nearly par- 

 allel to the plane of the valves ; foramen triangular, appearance of 

 crenulations as in the other valve ; wrinkles not so plain. 



Surface of both valves marked by fine radiating striee, about every 

 fourth or fifth one stronger than the others, which extend from the 

 hinge line about two thirds or three fourths of the distance to the free mar- 

 gins, Avhere they are interrupted by rough eleviitions (generally most so 

 on the ventral valve), continuing to the edge of the valves, which are 

 much thickened up. This roughness does not extend in all cases to 

 the lateral margins, iimnediately in front of hinge line, and in the doi-sal 

 valve it is sometimes entirely wanting. It is found on the small, 

 young shells as well as old ones. 



Figures referred to this species are published in the Pal. of Ohio, 

 vol, i., part 2, plate 5, 3/ and Sg, but they do not show the rough 

 surface ; the radiating strise being made to continue to the free mar- 



gins. 



Leptcena rugosa (a synonym) was pre-occupied for another shell — now 

 known as Strophomena tenuistriata (Sowerby) — hence the change of 

 name. 



