SPIRIFERA. 35 



pi. xxxviii, fig. 6, of the ' Geol. Transactions,' above quoted ; which figures resemble 

 likewise the original ones of hystericus published by Schlotheim. 1 cannot, however, 

 understand why Sowerby should have made use of the term Sp. micropterus, Goldfuss, for 

 his specimens, since he admits that they agree with Hysterolites hystericus, but which 

 last he stamps as a synonym of Sp. micropterus. 



We may now inquire what is H. hystericus, Schlotheim ; and, in the absence of any 

 description or well-authenticated specimen, the question can be answered only by a close 

 examination of the author's figures. These consist of internal casts of the dorsal and 

 ventral valves of a Spirifer imbedded in a slab of shale or grit, and which will answer to the 

 following description : 



Shell transversely semicircular or sub-pentagonal ; hinge-line about as long as the 

 width of the shell ; valves convex, with a smooth mesial fold in the dorsal valve, to which 

 corresponds a similar sinus in the opposite one ; surface of each valve ornamented by some 

 twenty angular ribs, the widest of which does not much exceed one line in breadth ; length 

 14, width 20 lines; and this description would suit equally well to our Linton specimens. 

 It has been said that the surface of H. hystericus was crossed by concentric lines or laminae 

 similar to those of Sp. speciosa and of other species ; but these are not observable in 

 Schlotheim's figures of internal casts any more than they could be seen on the Linton 

 specimens, and may have been present in both had we the shell itself to examine. The 

 subject of this identification must remain an unsettled question until more perfect material 

 and direct comparisons can be effected between our Linton specimens and Schlotheim's 

 original ones of hystericus. 



? Spirifera cultrijugata, Eoemer. PI. VIII, figs. 1, 2, 3. 



Spirifer cultrijugatus, Roemer. Rheinisch. Uebergangsgeb., p. 70, pi. iv, fig. 1, 1844. 



— — Roemer. Beitrage zur geologischen Kenntness der nordwest- 



lichen Harzgebirges, in Dunker's Palseontographica, pi. xv, 

 1852. 



— — Schnur. Palseontographica, vol. iii, pi. xxxiii, fig. 1, 1853. 



— — Sandberger. Die Brachiopoden der Rbeinischen Scbich ten- 



systems in Nassau, pi. xxxii, fig. 4, 1855. 



Spec. Char. Shell large, transversely semicircular ; hinge-line usually rather shorter 

 than the width of the shell ; dorsal valve convex, at times gibbous, with a large prominent 

 fold or central rib, and six or seven strong simple ribs on each of the lateral portions of 

 the valve ; ventral valve convex, with a similar number of ribs and a wide median sinus ; 

 beak of moderate proportions, and incurved ; area triangular ; fissure large, partly arched 

 over by a pseudo-deltidium ; proportions variable, two British specimens have measured — 



Length 1 inch 10 lines, breadth 2^ inches. 



„ 2i inches, „ 3 inches 9 lines. 



