BRACHIOPODA. 
Shell .mequivalyed, convex or concayo-conyex, externally 
striated ; hinge line rather shorter than the width of the shell; 
ilorsal valye semicircular, with a small narrow area. Ventral 
valye with a prolonged and oftentimes bent beak; area trian- 
gular, with a fissure covered by a convex pseudo-deltidium. No 
foramen is observable, but the cardinal process is at times seen 
partially extending under the deltidium (Fig. 26). 
Interior of ventral valve, with a strong hinge-work on either 
side at the base of the fissure, supported by a dental plate 
(Fig. 25, ¢); muscular scars two, elongated, oval, deeply exca- 
vated, separated by a wide mesial ridge (Fig. 26, 7). 
Interior of dorsal valve with a largely developed cardinal 
process, composed of two projections, grooved or bidentated 
towards the extremity of their outer surface; socket plates 
large, and partly united to the lower portion of the cardinal 
process; adductor scars quadruple, occupying more than a 
third of the length of the valve, and arranged in pairs, divided 
by a short rounded mesial ridge. 
This genus is intermediate between Orthis and Strophomena. 
Distribution, 6 species. Sil.—Perm. Europe, Asia, America, 
and Australia. 
TROPIDOLEPTUS, Hall, 1859. 
Etymology, tropis, a keel, and leptos, thin; the carinated 
ventral valve and shallow visceral cavity, in its analogy with 
Leptena. (See ‘‘ Reg. Rep.,”’ 1856, p. 3.) 
Type, Strophomena carinata, Conrad. 
Shell transversely oval, or longitudinally semi-elliptical, 
articulating by teeth and sockets, hinge line about equal to the 
breadth of the shell. Ventral valve convex, with a linear area 
and triangular foramen in the margin of the area; from the inner 
edges of this proceed the dental lamellee, which are separated 
from the area by a narrow grooye strongly crenulated on the 
outer edge, and extending obliquely outwards, terminating ina 
low ridge which partially surrounds the muscular impression ; 
dorsal vyalye concave; cardinal process prominent, wedge- 
shaped, supporting the bases of the crura; dental fossets crenu- 
lated, surface plicated; shell structure punctated. 
Distribution, 2 species. Devonian. United States. 
VitTuLina, Hall, 1861. 
Etymology, Vitula, a goddess. 
Type, V. pustulosa, Devonian. New York. 
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