BRACHIOPODA. 379 
CUtambonltes diversal 
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 adjustor 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 
