STROPHOMENID^. '317 



is the socket. Under the cardinal process a rounded ridge separates the obscurely 

 marked muscular impressions (fig. 13). The whole inner surface of both valves is 

 furrowed by numerous fine striae, as well as by some few concentric lines of growth. 

 Length 12, width 13, depth 1 line. 



Obs. This variety (?) of Strophomena compressa seems to me to difier more from its 

 type than St. compressa differs from St. expansa. It belongs also to a lower geological 

 stage. I have consequently thought it preferable to distinguish (at least provisionally) 

 it by a varietal designation. It is of a more lengthened semicircular form than is St. 

 compressa, and its interior details vary in several particulars. 



Position and Locality. This form occurs in the Upper Llandeilo Flags at Lann Mill, 

 near Llandeilo, Caermarthenshire. It was also found by Mr. Morton at Bog-Mine, near 

 Shelve, and in some other localities. 



As Strophomena compressa lived in the Caradoc and Llandovery periods, this shell, if 

 a variety of that species, would be its most ancient form. 



Strophomena Fletcheri, Dav. (sp.). PI. XL VII, figs. 5 and 6. 



LEPTiENA Fletcheri, Davidson. London Geol. Journ., vol. i, p. 12, pi. xii, figs. 9 and 

 10, 1847; and Bull. Soc. Geol. France, ser. 2, toI. v, pi. lii, 

 fig. 12, 1848. 

 — — De Fernenil. Ibid., p. 347. 



Spec. Char. Semicircular, wider than long, greater breadth at the straight denticulated 

 hinge-line ; cardinal extremities extended into pointed mucronate wings ; sides and 

 front rounded. Ventral valve very obliquely and moderately convex ; beak small, 

 incurved, scarcely projecting ; area very narrow ; fissure small, arched over by a convex 

 pseudo-deltidium. Dorsal valve concave, following the curves of the opposite valve; 

 hinge-area linear. Surface of both valves covered with numerous, but very slightly 

 defined, thread-like radii, which increase in number by the interpolation of smaller striae. 

 Interior not known. 



Length 7, width 12, depth 1 line. 



Obs. In 1847 I described this species as a Leptcena, but I think it will be more 

 correctly placed with Strophomena. It is easily distinguished from Leptana transversalis 

 (with which species it has been erroneously confounded by Mr. Salter), both by its shape 

 and its striation. In L. transversalis the beak is very prominent and greatly incurved, 

 while in Strophomena Fletcheri it is very small and scarcely projecting. The convexity 

 and concavity of its valves are also much less than in Leptcena transversalis ; and it was 

 at once recognised as quite distinct by MM. de Verneuil and D'Orbigny in 1848. In 



