BRACHIOPODA. 379 



Clltambonltes dlversal 



more or less abruptly into the broadly-rounded and centrally somewhat sinuous, 

 anterior edge. Surface marked with numerous, subangular, prominent, sometimes 

 tubulose striae, increasing in number by interpolation and bifurcation; from seventy 

 to eighty-eight in adult examples along the margin and crossed by crowded, delicate, 

 concentric growth lines some of which imbricate near the outer margin. 



Ventral valve strongly and evenly convex, with the point of greatest elevation 

 near the beak. Cardinal area very wide, broadly triangular, flat or elevated, and 

 slightly convex, distinctly striated longitudinally and finely transversely; deltidium 

 broadly triangular, strongly convex, with a large oval pedicle opening in the apical 

 portion; anterior margin broadly excavated and, when perfect, completely occupied 

 by the chilidium of the dorsal valve. On the interior the dental processes are not 

 very large and are attached to the strong lamellae, which converge and join centrally 

 before reaching the bottom of the valve, forming the spondylium, which is supported 

 by a well-developed septum terminating in the anterior third of the valve. The 

 upper surface of the spondylium has a narrow median depression, which is some- 

 times faintly divided by a fine line; the lateral limits of this plate are also slightly 

 depressed, and the whole is crossed by numerous transverse lines of growth. The 

 lines have a constant curvature in the median depression, with another over the 

 area on each side and are strongly reflexed along the edge of the delthyrium. These 

 markings are believed to be due to the adductor, diductor and adjuster muscles, 

 which were attached to the upper surface of the spondylium, as not the slightest 

 trace of any scar can be seen on the under surface of this plate, nor on the valve 

 immediately beneath it. Genital markings numerous, delicate, originating under- 

 neath the spondylium, radiating towards the antero-lateral margins and surrounded 

 by the vascular sinuses. Outside of the latter there is a smooth space, while the 

 anterior margin of both valves is slightly marked by radiating lines. 



Dorsal valve slightly concavo-convex, or almost flat; point of greatest elevation 

 at the apex, where a shallow, narrowly-expanding medial depression has its origin 

 and extends to the anterior margin. Cardinal area conspicuous but not wide, cen- 

 trally occupied by a broad, short and strongly elevated chilidium. Underneath the 

 latter, and attached to it, is what may be termed a simple cardinal process. The 

 muscles are not attached to the top of this process, as in species of Orthis, but to the 

 striated thickening of the rostral cavity and slightly to the basal portion of the 

 process, the whole being covered by the chilidium. Dental sockets prominent, situ- 

 ated at the point of union of the cardinal area with the chilidium. The crural plates 

 form the inner edges of these sockets, are much elevated and continuous with the 

 deltidium. The rostral thickening extends forward as a broad, low septum to near 

 the center of the valve, and on each side are two strongly excavated, separate pairs 



