STROPHOMENIDtE. 299 



Salter (not Pander) ; and have placed the species so named, with some uncertainty, in 

 the genus Strophomena. It is not an Orthis any how ; for its fissure is arched over with 

 a pseudo-deltidium, such never being the case in the true Orthides. The dorsal valve being 

 flat or slightly convex is likewise a feature not characteristic of Strophomena, but it 

 may be here an exception to the rule ; and until we are acquainted with its interior 

 the shell cannot be definitely referred to its proper place. 



Position and Locality. The specimens in the Museum of the Geological Survey were 

 obtained from the Caradoc at the Chair of Kildare, in Ireland, It has also been found 

 in rocks of a similar age near Girvan, in Ayrshire. 



Strophomena antiquata, Soiu. (sp.). PI. XLIV, figs. 2 — 13, and 21, 22. 



Orthis antiquata, J. de C. Sow. Sil. Syst., pi. xiii, fig. 13, 1839. 



— — Dav. Lond. Geol. Journ., vol. i, p. 62, pi. xiii, fig. 25, 1847. 



Lept.ena Lewisii, Dav. Ibid., p. 59, pi. xii, figs. 22 — 24, 1847. 

 Orthis scabrosa, Dav. Ibid., p. 61, pi. xiii, figs. 14, 15, 1847. 

 Lept^ena antiquata, Dav. Bull. Soc. Geol. France, ser. 2, vol. v, p. 319, pi. iii, fig. 

 11, 1848. 

 — — Phillips and Salter. Mem. Geol. Surv., p. 283, 1848. 



Strophomena antiquata, D'Orb. Bull. Soc. Geol. France, ser. 2, vol. v, p. 336, 1848. 

 Lept^na (Strophomena) antiquata, M'Coy. Brit. Pal. Foss., p. 241, 1852. 

 Strophomena antiquata, Salter. Siluria, 3rd edit., pi. xx, fig. 18, 1859. 



— SCABROSA, Lindstrdm. Gotl. Brach., p. 372, 1860. 



— ANTIQUATA, Dav. Trans. Geol. Soc. Glasgow, Pal. Ser., vol. i, p. 17, 



pi. ii, figs. 21— 23, 1868. 



Spec. Char. Varying much in shape, according to age and individual; truncato- 

 elliptical, semicircular, or subtrigonal, wider than long ; hinge-line nearly or quite as 

 long as the shell is wide ; cardinal extremities obtusely or acutely angular ; sides 

 usually rounded, and converging to sometimes a narrow obtusely rounded front. Ventral 

 valve slightly concave, with a deeper depression along the middle, and gently convex 

 at the beak. In some examples a small circular foramen exists close to its extremity. 

 Area rather narrow, fissure in the centre, arched over by a triangular pseudo-deltidium. 

 Dorsal valve moderately convex, gently curved in profile, flattened posteriorly, or in the 

 vicinity of the umbonal beak and cardinal extremities ; while a median elevation or fold 

 rises, in some specimens, towards the middle of the valve, and becomes more elevated or 

 pinched (as it were) as it nears the front, thus producing a raised rounded wave at the 

 frontal margin. Hinge-area narrow, about one third of the length of that in the opposite 

 valve, and possessing in the middle a convex pseudo-deltidium which corresponds with 

 that in the opposite valve. External sculpture variable in its details, but always radiated 



