STROPHOMENIDtE. 307 



depression is rather large and longitudinally divided along the naiddle by a ridge. Interior 

 of dorsal valve not known. 



Length 13, width 20 lines. More often only half that size. 



Obs. In 1848 I described this shell as an OrtJiis ; but its true place is with Stropho- 

 mena. In shape it most approaches Stropli. peden ; but differs from it in the shape of its 

 muscular impressions, as may be at once perceived by comparing the interior of the ventral 

 valve in both species. D'Eichwald, in his 'Lethsea Rossica/ p. 3G5, considers it to be 

 a variety of St. pecten, or rather of the Orthis jilitexta of Hall. 



Position and Locality. I found several examples of the ventral valve in the Wenlock 

 Limestone at Dudley; and a large incomplete specimen from the same locality (fig. 13) 

 may be seen in the Museum of Practical Geology. 



Strophomena filosA; /. de C. Sow. (sp.), PI. XLIV, figs. 14 — 20, 



Orthis filosa, J. de C. Sow. Sil. Syst., pi. xiii, fig. 12, 1839. 



— — M'Coi/. Synop. Sil. Foss. Ireland, p. 30, 1846. 



— — Dav. Lond. Geol. Journ., vol. i, p. 62, pi. xiii, fig. 24, 1847. 

 Lept^na — Dav. Bull. Soc. Geol. France, ser. 2, vol. v, p. 318, pi. iii, fig. 9, 



1848. 

 Orthis — Phillips and Salter. Mem. Geol. Surv., vol. ii, p. 288, 1848. 



Strophomena — Salter. Mem. Geol. Surv., vol. ii, p. 380, 1848. 

 Lept/Ena — M'Coy. Brit. Pal. Foss., p. 243, 1853. 



Strophomena— Salter. In Siluria, 3rd ed., pi. xx, fig. 21, 1859. 



— — Schmidt. Sil. Form. Ehstl. ; in Arch. Nat. Liv- Ehst- und Kur- 



land, p. 216, 1858. 

 Lept^na — D' Eickioald. Lethsea Rossica, p. 873, 1859. 

 Strophomena — Lindstrom. Gotland's Brachiopoder, p. 373, I860. 



— — Salter. Mem. Geol. Surv., vol. iii, p. 279, 1866. 



Spec. Char. Semicircular, much depressed, wider than long, greatest width at the 

 hinge-line ; cardinal extremities sometimes slightly prolonged into angular mucronate 

 wings ; lateral and frontal margin rounded. Ventral valve very slightly convex, almost 

 flat ; area narrow ; fissure small, arched over by a pseudo-deltidium ; beak not protruding. 

 Dorsal valve very slightly concave or flat ; hinge-area linear — surface of both valves covered 

 with numerous, thread-like, raised radii; a smaller riblet interpolated between each 

 pair of the larger ones. In the interior of the ventral valve a small hinge-tooth is 

 seen on each side of the fissure; muscular impressions large, fan-shaped, and 

 arranged in four longitudinal oval depressions ; a narrow median ridge extends along 

 the middle of the valve for about one third of the length of shell. In the interior of the 



