864 Report oF THE State GEOLoaIsT. 
In the brachial valve the dental sockets are quite deep and 
narrow, the socket-walls rising abruptly, though not attaining 
the height of the dental plates of the opposite valve. They are 
distinctly separated from the crural plates or 
margins of the hinge-plate, and converge toward 
the apex, where they merge into a slightly elevated 
cardinal process; the latter usually appearing 
Rsk isi Pe ea, as a crescentic submarginal wall, though when 
ton, An enlarg- best preserved is seen to be composed of two 
pment oF tina ot lateral, somewhat rounded lobes. The crural 
the brachial valve, plates are two divergent vertical lamellx, origin- 
Wr thixened to. ating just below the cardinal process, and attain- 
cesses oneither side ing a length equal to the distance between their 
behest as extremities, which is about one-third the width of 
the valve at that point. Between these plates lies the long, 
shallow hinge-plate, which is raised but little above the bottom 
of the valve, and is sometimes actually adherent to it. This 
plate attains its greatest width at the extremities of the vertical 
crural plates, its margins converging thence anteriorly, its full 
length often equaling one-third that of 
the valve. To this plate are attached all 
the muscles of the brachial valve, the 
scars of both anterior and posterior 
adductors being frequently clearly de- 
fined upon its surface. The lateral 
divisions of the plate have become 
merged with the valve and lost. The 
median division, which is also to a cer- : 
: E 5 Fie. 501. Dielasma elongatum, 
tain extent myiferous in CRyYPTONELLA, Schlotheim. The interior of the 
is carried to an extreme of develop- Aeeee, he Ge ae 
ment in Dietasma, where it forms a dental plates (d), the elongate, 
distinct platform. The crura are wee aiid ae Seema eae 
greatly abbreviated. The descending attachment of the brachidium. 
lamelle of the brachidium are attached ©*"*°*? 
to, and are continuous with the crural plates, as far as the latter 
extend. The crural apophyses on the upper margins of these 
lamellae are developed behind the points where the lower 
margins of the lamelle are free from the crural plates. The 
lateral parts of the brachidium are more or less divergent 
the recurvature of the ascending lamelle rather short and the 
116 
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