STROPHOMENID.E. 311 



Strophomena Hendersoni, Dav. PI. XLIII, fig. ] 5. 



Strophomena Hendersoni, Dav. Trans. Geol. Soc. Glasgow ; Pal. Series, Fasc. 1, 



p. 19, pi. ii, fig. 24, 1868. 



Spec. Char. Semicircular, wider than long, greatest breadth at the hinge-line ; 

 ventral valve very slightly convex ; dorsal valve gently concave. Surface covered with 

 numerous, exceedingly fine, hair-like, radiating, raised striae, closely imbricated by still 

 finer and closer concentric lines. 



Length 5, width 7 lines. 



Obs. Of this species I have seen two examples, which were obtained by Mr. J, 

 Henderson in Wenlock Shales, North Esk, Pentland Hills, Scotland. This shell is 

 remarkable on account of the extreme minuteness of the imbricating striae which adorns 

 its external surface. The interior has not been yet discovered. 



Strophomena grandis, Soio. (sp.). PI. XLVI, figs. 1 — 3 and 5, 6. 



Orthis grandis, J. de C. Sow. Sil. Syst., pi. xx, figs. 12 and 13, 1839, 



— — M'Coy. Sil. Foss. Ireland, p. 31, 1846. 



Lept^na (Strophomena) grandis, M'Coy. Brit. Pal. Foss., p. 244, 1852. 

 Strophomena grandis, Salter. In Siluria, 3rd ed., pi. vi, figs. 6 and 7, 1859. 

 Lept^na — Morris. Catal. Brit. Foss., p. 137, 1854. 



— — D'Eichwald. Lethsea Rossiea, vol. i, p. 864, 1859. 



Spec. Char. Semi-oval, or truncato-elliptical, wider than long; hinge-line either 

 slightly shorter than, or as long as, the shell is wide ; cardinal extremities rectangular, 

 or obtusely angular; sides and front rounded. Ventral valve slightly convex at the 

 beak, but becoming gently concave about the middle and towards the margin ; area 

 narrow ; fissure arched over by a small pseudo-deltidium. Dorsal valve gently convex ; 

 area narrow. Surface of both valves ornamented with numerous, strong, prominent, 

 thread-like radii, with one or two smaller and shorter ones filling up the interspace left 

 between the principal pairs. The surfaces of the valves are crossed by numerous, close 

 and fine, concentric, raised lines. In the interior of the ventral valve the muscular 

 impressions are rather narrow, elongated, and divided in the middle by a rounded ridge 

 (fig. 3). Interior of the dorsal valve not known. 

 Length 22, width 27, depth 3 lines. 



Obs. This species is at once distinguished from Strophomena expansa and St, 



