CYPRICARDELLA ACUTICARINATA. 359 



From the point near the shooting box the section is continued downwards in the stream, of 

 which details have also been given in the ' Memoir of the Geological Survey, Geology of the Country 

 round Mallerstang,' p. 83. Two beds of Limestone are seen in the section, which are identified as 

 the Five Yards and the Middle Limestone, here full of Productus giganteus. This would make the 

 Limestone immediately below the fossil if erous shales the Underset, and would fix the horizon of that 

 band; but in a brook on the east side of Swarth Fell a series of fossiliferous shales are above the Main 

 Limestone, and the faunas of the two localities are very nearly identical, though this fact only points 

 to similarity of conditions under which the beds were deposited. 



The following fossils occur with C. rectangularis -. — Cypricardella Annie, Nuculana attenuata, 

 Ctenodonta sinuosa, Pecten, sp., MurcTiisonia, sp., Discites, sp., Productus semireticulaius, P. punc- 

 tatus, Spirifera trigonalis, Sp. ovalis, Athyris ambigua, Streptorhynchus crenistria, Discina nitida, 

 stems of encrinites, and Phillipsia, sp. 



Cypricaedema acuticarinata, Armstrong, sp., 1865. PI. XXXIX, figs. 14 — 19. 



Cypricardia acuticarinata, Armstrong, 1865. Trans. Geol. Soc. Glasgow, 



vol. ii, pt. 1, p. 28, pi. i, figs. 3, 3 a. 



— Young and Armstrong, 1871. Ibid., vol. iii, Sup- 



plement, p. 50. 



— Armstrong, Young, and Robertson, 1870. Cat. 



Western Scottish Fossils, p. 53. 

 Bigsly, 1878. Thesaurus Devonico-Carbonif'erus, 

 p. 203. 

 Sanguinolites acuticarinata, de Koninck, 1885. Ann. Mus. Boy. d'Hist. Nat., 



torn, xi, p. 63, pi. xv, figs. 48 — 50. 

 Cypricardia acuticarinata, Etlieridge, 1888. Brit. Foss., pt. 1, Palaeozoic, 



p. 282. 



Specific Characters. — Shell subtrapezoidal, at times almost quadrate, very 

 inequilateral, strongly cariuate. The anterior end is very short and low, and 

 compressed, its border rounded, much encroached upon above by the com- 

 paratively large lunule. The inferior border is convexo-concave, and terminates 

 posteriorly at a sharp-pointed projection where it meets the posterior border. 

 The posterior border is truncated, slightly oblique from above downwards or 

 even vertical, concave above ; it joins the posterior border with a well-marked 

 angle, which may project slightly backwards. 



The superior border is shorter than the antero-posterior diameter of the shell, 

 and appears to be straight for the greater part of its extent, but it is really 

 gently arcuate when examined -in the single valve. 



The umbones are small, contiguous, pointed, twisted inwards and forwards, 

 and are situated very far forwards. Springing from the posterior edge of the 

 umbo is a very marked, raised, narrow, sharp, erect ridge, which passes obliquely 

 downwards and backwards to the postero-inferior angle, becoming more pro- 

 nounced as it passes across the shell. This ridge divides the valve into two 



