Brachiapoda of the Cincbinati Group. 57 



Leptena sericea — (Sowerby, 1839). 



Transversely oblong, substance of the shell thick, very coarsely 

 fibrous; hinge line slightly exceeding the width of the shell; cardinal 

 angles acute, sides gently convex, slightly converging; front nearly 

 straight, wide ; receiving valve much and regularly arched to the 

 deflected margins ; greatest depth at one third from the beak ; enter- 

 ing valve slightly flattened in the rostral portion, rather abruptly arched 

 to the margin ; greatest depth at two thirds from the beak ; often 

 a few small, converging wrinkles on each ear ; both valves radiated 

 with extremely fine, haii--like strise, separated by sulci ecpialing them 

 in size, containing close rows of very minute punctures ; at mtervals 

 of from one half to one fourth (near the margin) of a line apart 

 certain of the striae become about twice the size of the others, including 

 betAveen each pair from five to ten smaller ; about thirteen to sixteen 

 striae in the space of one line, in the middle of front margin, at 

 three Imes from the beak; cardinal area in each valve low, triangular; 

 that of the receiving valve about a third larger than that of the 

 entering valve ; rostral tooth very large, five-lobcd, nearly filling the 

 triangular foramen of the receiving valve, which is as Avide as high, 

 and the apex of which is closed by a small deltidium ; internal cast of 

 receiving valve showing two very short cardinal teeth bordering the 

 triangular boss of the foramen, diverging at about 135°, from the ends 

 of which proceed two longitudinal, slightly incurved, slightly diverg- 

 ing ridges (forming slight furrows on cast), forming the outer boundaries 

 of two long, prominent, obtusely ovate muscular impressions, wide, 

 and only separated near the beak by a very slender sulcus of a mesial 

 septum, scarcely one third the length of the shell; anterior boundaries 

 sharp, diverging at about 70°, inclosing between them a prominent 

 semi-eliiptical mesial space, and narrowing the anterior ends of the 

 muscular impressions, from each of which extend four or five thick 

 diverging and dichotomising impressions of the pallial and ovarian 

 vessels, a couple of similar dichotomising impressions on each side of 

 the mesial space, and three or four very short ones on each lateral 

 margin ; the rest of the surface marked with obscure traces of the 

 external striffi, punctured in lines, the punctures becoming much 

 larger at the margin, between the branches of the pallial vessels; 

 interior of entering valve concave for two thirds the length from the 

 beak, the margin abruptly arched over, very closely punctured (not 

 in rows), and marked at the edge with numerous, short, simple ridges; 

 two very short cardinal teeth diverge from the rostral tooth ; muscular 



