BRITISH SILURIAN BRACHIOPODA. 113 



persistent few strong scabrous ribs. Young species of A. reticularis of similar dimensions 

 differ from it materially, and if one looks at Schlotheim's figures of his Terebratulites 

 aspera in pi. i of Leonhard's ' Tashenbucli ' for 1813, the difference is obvious, Schlotheim's 

 figures recalling certain small varieties of Atrypa reticularis. I therefore propose to 

 distinguish the species under description by a separate name, that it may no longer be 

 confounded with Linne's species. 



12. Atrypa marginalis, Dal. Dav., Sil. Mon., p. 133, PI. XV, figs, 1, 2; Sil. Sup., 



PI. VII, figs. 8, 8 «, 8 h, 



"We are indebted to Mr. Glass for the knowledge we now possess with respect to the 

 spiral appendages and connecting process in this remarkable s})ecies. 



The dorsal valve does not present the same degree of convexity or depth observable 

 in Atrypa reticularis, so that the spirals are smaller, and less convex. They do not 

 show more than five convolutions, these being also more widely separated one from 

 the other than is the case with Linne's species. The principal stems (in the two 

 specimens cleared out by the Rev. Norman Glass) after their attachment to the hinge- 

 plate are soon connected, as in A. reticularis, by a V-shaped lamella. The extremities 

 of the spirals are close to each other and face the middle portion of the bottom of the 

 dorsal valve. As in Atrypa Barrandei, the two principal coils 

 are not level, but slightly higher on their inner than on their 

 outer sides. 



Mr. Glass has also shown that the outer edge of each 

 convolution, whether facing the lateral or the frontal margin of 

 the shell, gives off numerous small spiny projections, in the 

 same manner as in many examples of Spirifera, Athyris, Wald- 



hpimin Rrr Atrypa marginalis, developed 



neimia, CZC. ^^, ^^^ ^^^ Norman Glass, 



While Atrypa reticularis and A. Barrandei are exceedingly ^^^ enlarged. 

 abundant in the Wenlock series of Shropshire, A. maryinalis and A, imbricata, Sow., 

 are by no means common. 



