6s 



center ; along the median line the shell is somewhat more remarkably folded. 

 This median fold ends in a beak, small and pointed, but projecting only a very 

 little beyond the hinge-line. Dorsal valve lacking. The surface of the shell 

 is decorated with very fine radial stria; that look like bundles of silk. At re- 

 gular intervals there are much coarser striae among them ; these are also 

 visible to the naked eye. The stri?e, both fine and coarse, increase in number 

 anteriorly. There are several stages intermediate between the stronger striae 

 observable without the aid of a magnifying glass ; for they come into existence 

 at various distances from the beal-c, in accordance with the growth of the shell. 

 The silky striae or radii are granulate and intercrossed by equally minute con - 

 centric lines which may be called growth lines. 

 Dimensions 



Length. Width. Thickness. 



9 mm. 14 mm. 3 mm. 



II mm. 15 mm. ? 



Remarks : — In the present fossils the beak is very small, only very 

 slightly projecting, and the punctures on the surface of the shell are extremely 

 minute. The form also is more transverse than P/ir. traiisvcrsalis, for 

 Davidson gives, for instance, as the proportion of the length, width and depth 

 9, II, I. The shell is rather more flattened than in the latter species. Ac- 

 cording to Davidson the chief distinction between these two very resem- 

 blant species lies in the difference of the shape of the muscular impressions. 

 He says that they are expanded and flattened in Plec. scricea while they are 

 convex in the other. This difference, however, has not been detected in the 

 Chinese examples. As far, however, as the specimens accessible are con- 

 cerned, the present fossil most resembles the species Plcc. sericca, although 

 there are several allied forms of the genus known. Even among a number 

 of species of the group illustrated by Barrande^' the most resemblant is 

 nothing but his Leptaena transvcrsalis, \M\\\c\\, however, is less allied to the 

 Chinese fossil than Plec. scricea is. 



Locality : — Kao-huang-ling, Hsing-shan-hsien, I-chang-fu, prov. Hu-pei. 

 In association with Triplccia poloi and several other brachiopods of which the 

 determination is not possible. 



