264 CARBONIFEROUS LAMELLTBRANCHIATA. 



C. obliqua appears to be very rare. I have only met with the species in the 

 two localities mentioned above. 



Caediomorpha orbicularis, M'Coy, 1853. Plate XXII, figs. 1, 3 — 7. 



Caediomoepha oebiculaeis, M'Coy, 1853. Ann. and Mag. Nat. Hist., ser. 2, 



vol. xii, p. 189. 



— — — 1855. Brit. Pal. Foss., p. 510, pi. 3 1, 



figs. 41, 41 a. 



— — Bigsby, 1S78. Thesaurus Devonico-carbonif., p. 301. 



— globata, de Koninck, 1885. Ann. Mus. Eoy. Hist. Nat. Bel- 



gique, vol. xi, p. 15, pi. iv, figs. 3, 4. 



— Soweebtt, de Koninck, 1885. Ibid., p. 15, pi. iv, figs. 5, 6 ; pi. 



xii, figs. 21, 22. 

 Cf. — teapezoidalis, de Koninck, 1885. Ibid., p. 15, pi. iv, figs. 9, 10. 



— subquadeata, de Koninck, 1885. Ibid., p. 16, pi. viii, figs. 1 



and 2. 



— oebiculaeis, Etheridge, 1888. Brit. Foss., vol. i, Palaeoz., p. 281. 



Specific Characters. — Shell large, suborbicular, gibbose, almost equilateral. 

 The anterior end is comparatively large, compressed, especially at the antero- 

 superior angle, where it is concave ; its border is semicircularly curved. The 

 ventral border is also regularly curved in front, and behind it passes into the 

 posterior border without a break. The posterior margin is short and convex, 

 the segment of a smaller circle than that which forms the anterior, the posterior 

 side being smaller than the anterior and gradually compressed. The hinge-line 

 anterior to the umbo is straight, but the posterior portion is regularly arched and 

 rapidly depressed, the whole extending across the shell, of which it forms the 

 longest transverse diameter. The umbones are very large, tumid, elevated above 

 the hinge-line, markedly twisted inwards and forwards, contiguous ; the apices 

 are depressed, everted, and curved spirally on themselves. They are almost 

 median in position, and somewhat oblique. There is no lunule. The valves are 

 regularly convex, but become gradually compressed towards the margins. The 

 valves attain the greatest degree of convexity at a point on a level with the 

 hinge-line. 



Interior. — The anterior and posterior adductor muscle-scars are very shallow 

 and inconspicuous. The former is large, orbicular, and situated just within the 

 antero-superior angle ; the posterior, almost obsolete, is just below the posterior 

 extremity of the hinge-line. The pallial line is simple and remote from the 

 margin. The hinge is thin and linear in front of the umbo ; a hinge-plate 

 is developed behind at right angles to the shell, corresponding to a deep 



