SPmiFERID^. 



91 



(Shropshire, &c.) ; and the section of this west coast of Ireland is perfectly clear. 

 Spirifera hijugosa occurs chiefly in the condition of external and internal casts, and has 

 not been hitherto found in England, Wales, or Scotland. 



Spirifera sulcata, Hisinger. PI. X, figs. 4 — 6. 



Anomia crispa, LinnL Syst. Nat., 12th edit. p. 1152, 1767 ; and Mus. Tessin., p. 90, 

 tab. V, fig. 7, 1753. 



Delthyris sulcata, Hisinger. Anteckn. Physik. och Geognosi, p. 119, tab.iii, fig. 2, 

 1831. 



— — Ibid. Lethsea Suecica, p. 73, tab. xxi, fig. 6, a, b, c, 1837. 



Spirifer sl'lcatus, Davidson. Ball. Soc. Geol. France, 2nd series, vol. v, pi. iii, fig. 41, 

 1848. 



— — De Ferneuil. Ibid., p. 347, 1848. 



Spirifera sulcata, Lindstrom. Proceed. Roy. Acad. Sc. Stockholm, p. 359, 1860. 



Spec. Char. Transversely subrhomboidal ; hinge-line much longer than the width 

 of the shell ; cardinal angles pointed and extended ; while, not uncommonly, one wing 

 exceeds the other in length. Dorsal valve much less convex than the opposite one, 

 bearing three or foiu- principal ribs, of which the central one is both the largest and most 

 elevated, the remaining lateral space being either smooth, or provided with one or two 

 smaller or rudimentary ribs ; the three or five principal costae thus occupying either half 

 or two-thirds of the surface of the valve. Ventral valve much deeper than the dorsal, 

 with two or three ribs on each side of the sinus, which last is as broad as the width of 

 the mesial rib or fold in the opposite valve ; surface of both valves crossed by numerous 

 concentric projecting laminae, which overlap each other to a greater or lesser extent. 

 Besides these, the surface is covered with a delicate network of small minute longi- 

 tudinal and transverse striae, visible only by the assistance of a magnifying glass. 

 Beak slightly incurved ; area rather wide, triangular, and divided in the middle by a 

 fissure ; deltidium composed of two triangular plates, which rise abruptly from the lateral 

 margins of the fissure with their broadest extremities near the umbone of the dorsal 

 valve, thus leaving only a narrow oval aperture in the middle ; with age, this opening 

 becomes more and more diminished in extent. Two specimens measured — 

 Length 6, width 10, depth 4 lines, 

 „ 4, „ 5, „ 3 „ 

 but the shell is usually much smaller. It is a smaller species than Sp. crispa. 



Obs. It is sometimes difficult to distinguish certain varieties of Spirifera sulcata, 

 Sp. crispa, and Sp. elevata, the last two of which especially pass one into the other 

 to a perplexing extent ; nevertheless, when well shaped and full grown, they present 

 recognisable distinctions ; and palaeontologists generally have considered it desirable that 



