118 DEVONIAN FAUNA. 



the anterior point, rounded, proximate. Hinge-margin straight, about two-thirds 

 the length of shell. Margin running from beneath the umbo in a long, oblique, 

 straight or slightly flexuous line to the postero-inferior corner, which it rounds 

 in a broad parabolic sweep, and is continued back obliquely in a gentle convex line 

 to the rear of the hinge-margin. Greatest depth of shell near the umbo, and line 

 of greatest depth running from the umbo close to the front margins. Contour 

 of surface almost perpendicular on the antero-inferior slope, very convex on the 

 back, and gradually becoming slightly concave near the postero-superior corner, 

 so as to form a small undefined wing. 



Size. — About 15 mm. long by 12 mm. high. 



Locality. — One specimen from Brauuton is in the Museum of Practical Geology. 



Remarks. — The fossil above described is rendered rather obscure by the 

 encroachment of the matrix over its margins, but it evidently is of a very typical 

 mytiloid shape, and appears to be definitely unlike any other palaeozoic species. 



Affinities. — Cardiomorpha mytiloides, F. A. Romer, 1 seems to be a steeper and 

 differently shaped shell. 



Modiomorpha submissa, Barrande, 2 sp., as given by Barrois, 8 seems more trans- 

 verse, and has a narrower umbo and more dilate front side. 



Among other points the obliquity of the posterior side distinguishes it from 

 Leptodesma citimum. 



Mytilarca injlata, Whiteaves, 4 is somewhat like in shape and in the bluntness 

 of the umbo, but is shorter and more convex. 



Mytilus sabesianus, de Ryckholt, 5 appears to be shorter and more regularly 

 ovate, with a sharper umbo, and a shorter and more concave antero-inferior 

 margin. Isocardia contorta, Barrande, 6 may also be compared. 



II. Sub-family — AviculinjE, Stoliczlca, 1871. 



1. Genus — Cobeacephalus (Provisional genus). 



Shell inequivalve, inequilateral, oblique, with large front wing and dilate hind 

 wing. Umbo extending above the long straight hinge-line, arching forward and, 

 in the right valve, overhanging. Contour divided by five or six radiating angles, 

 spreading from the umbo or its neighbourhood to the margins. Surface marked 

 by crowded squared growth-lines. 



1 1860, F. A. Komer, 'Beitr. Harzgeb.,' pt. 4, p. 163, pi. xxv, fig. 14. 



2 1881, Barrande, " Syst. Sil. Boheme,' vol. vi, pi. cclviii, figs. 4, 1—7, Et. F. 



3 1889, Barrois, 'Mem. Soc. Geol. Nord,' vol. iii, p. 170, pi. xii, figs. 2—2 c. 



4 1891, Whiteaves, ' Cont. Canad. Pal., 'Vol. i, pt. 4, p. 293, pi. xxxviii, figs. 5 — 6 a. 



5 1851, de Ryckholt, ' Melang. Paleont.,' pt. 2, p. 85, pi. xvi, figs. 22, 23. 



6 1881, Barrande, 'Sys". Sil. Boheme,' vol. vi, pi. cclx, figs. 1, i—u, Et. E. 



