STROPHOMENIDtE. 305 



Orthis pecten, Quenstedt. Handb., p. 487, pi. xxxix, fig. 16, 1851. 

 LEPTiENA. (Strophomena) PECTEN, M'Coy. Brit. Pal. Foss., p. 245, 1852. 

 Strophomena pecten, Schmidt. Sil. Form. Ehstl. ; Arch. Nat. Liv- Ehst- und 



Kurland, vol. ii, p. 214, 1858. 

 Anomia — Hanley. Ipsa Linnaei Conch., p. 125, 1855. 



Lept^na — D'Eichwald. Lethsea Rossica, Per. Anc, vol. i, p. 867, 1859. 



Strophomena — Salter. In Siluria, 3rd ed., p. 251, fig. 3, 1859. 



Orthis minuta, Haswell. Sil. Form. Pentlands, pi. iii, fig. 1, 1865. 

 Strophomena pecten, Dav. Pal. Trans. Geol. See. Glasgow, vol. i, p. 18, pi. iii, 

 figs. 1—4. 

 — — Lindstrom. Gotland's Brach., p. 373, 1860. 



Spec. Char. Shell transversely semicircular, broadish at its long straight hinge-line, 

 sides and front rounded ; cardinal extremities forming, with the lateral portions of the 

 valve, sharp acute angles. Valves much compressed. Ventral valve slightly convex at 

 the beak, but becoming gradually and gently concave as it approaches the margin ; area 

 triangular, of moderate width ; fissure in the middle arched over by a pseudo-deltidium ; 

 beak very small, scarcely projecting. Dorsal valve slightly convex, and flattened near its 

 cardinal extremities ; hinge-area linear, but with a small corresponding pseudo-deltidium 

 in the middle, so that the two, when combined, form a lozenge-shaped arch, widest and 

 most elevated at the hinge-line and tapering on all sides as it recedes near the extremities 

 of the beaks. Valves covered with numerous, thread-like, radiating, nearly equal ribs, 

 which increase rapidly in number by the insertion of one or two additional and finer radii 

 in the interspace left between each pair of larger ones ; the whole surface is likewise 

 closely crossed by numerous equidistant, slightly projecting, concentric ridges or lines of 

 growth. In the interior of the dorsal valve a small bifid cardinal process is situate 

 between two slightly projecting brachial (?) processes ; a short median ridge separates the 

 obscurely marked muscular impressions. In the interior of the ventral valve the muscular 

 impressions are scarcely defined. 



Length of a very large example 23, width 40, depth 3 lines. 



Obs. This species, although not then specifically named or described, was known to 

 Martin Lister as far back as 1687, a recognisable but incomplete figure having been ap- 

 pended to his small work ' Historise Animahum Anglise, Tres Tractatus (de Araneis, de 

 Cochleis terrestribus, et de Cochleis marinis),' London, 1678, pi. 9, fig. 49, and the 

 shell is stated to be fossil at Halifax. The figure was subsequently reproduced by the 

 same author, and in 1789 by Bruguiere. Linne was, however, the first to briefly 

 describe the shell, and his specific designation of "pecten" has been retained for it 

 by all subsequent naturalists. Linne says of his shell, " semiorbicular, depressed, with 

 numerous striae ; one valve flat : Lister, ' An. Angl.,' p. 243, pi. ix, fig. 49 : found in a 

 fossil state ; shell with a transverse line near the hinge." Since the time of Linnaeus it 

 has, however, been referred to the gtwexd^Terebratula, Orthis, Leptana, and Strophomena; 

 but with the first three it has no relation, and evidently belongs either to Strophomena 



39 



