BRAoHIOPODA. 871 
bilobed at its summit. Each of these lobes is excavated above 
so that the upper portion of the posterior wall is free from the 
rest of the process. In front of this is a broad, smooth floor, 
sloping toward the bottom of the valve. The margins of this area 
form the elevated socket-walls, and their anterior extremities are 
the bases of the crura. The dental sockets are deep and their 
outer walls corrugated for the reception of the teeth. The poste- 
rior portion of the sockets and the lower part of the cardinal pro- 
cess are covered by the erect, convex chilidium. At the anterior 
edge of the cardinal process lies a broad, thick, not elevated 
median ridge, which gradually narrows and becomes developed 
Tropidoleptus carinatus, Conrad. 
Fia@. 514. The interior of the brachial valve ; showing the cardinal process, crenulated dental 
sockets, loop and median septum. 
Fie. 515. The same in profile ; showing the height of the median septum and the mode of 
attachment of the lamelle of the loop. 
into a sharp, thin septum, attaining its highest point at about the 
center of the valve, whence it slopes rather more abruptly down- 
ward, terminating at the anterior third of the valve. From the 
crural bases extends a pair of long, slender lamellar processes, 
which curve outward, are directed upward, again converge and 
unite with the median septum on its lateral faces and just in front 
of its highest point. Slightly convergent, slender jugal processes 
are given off not far from the origin of the lateral lamellae. The 
scars of the adductor muscles are situated just in front of the 
cardinal process on either side of the septum, and are not clearly 
delimited. 
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