BRACHIOPODA. 
121 
structure of the hinge-plate and of the umbonal cavity of the pedicle-valve. 
The latter contains an internal tube attached by one side to the deltidium, and 
split along the opposite side, a precisely similar structure to that observed in 
Retzia Adrieni and Acamhona Osagensis, though not so highly developed as in the 
first of these. This structure is of so frail a nature ^ 
that it is difficult to preserve it in prepared inte- 
riors of the valve, but it always reveals itself in 
transverse sections of the beak near its apex. The 
structure of the hinge-plate has been quite accu- outline profile oSsfeim Mormom, m.ii- 
.11 *111 1 -v jifei' • L ' n cou, with enlarged transverse sections 
rately described by Derby=*^ from the interiors of of the umbo beneath the foramen; 
77 J ,. j. Tr r TT i j' Ti/r •\ ^ ^ showing the internal tube adherent to 
Lumetna punctulijera {=nustedia Mormom) obtained the coalesced deitidiai piatcs. (c.) 
from the limestone of the Coal Measures at Bomjardim, on the Amazonas. Dr. 
Waagen has also given a very accurate account both of the hinge-plate 
and the brachidium in species which he has referred to EuMETRiA.f The 
hinge-plate, as it appears in the preparations of Terehratula Mormoni, is con¬ 
stituted as follows; It is erect and recurved into the umbonal cavity of the 
pedicle-valve, projecting considerably beyond the hinge-line; the upper face is 
convex and elevated medially, the posterior margin sinuate and crescentic, 
though the horns of the crescent are very short; two deep converging grooves 
pass over the upper face, and outside of these, on the lateral margin of the 
plate are strong lobes which bear the erect, slightly recurved crura; from the 
crural bases the lateral margins curve downward to the bottom of the valve 
and form the socket walls. At the base of the cardinal process and in the 
median line arises a free, slender, ligulate process which curves upward and 
backward with a somewhat less curvature than the plate, and rises to the high¬ 
est point attained by the latter; the inner surface of this process is deeply 
grooved, and at its base it is supported by a median septum which extends for 
one-third the length of the valve. There is no tent-shaped structure for the 
support of the crura as in Eumetria. 
Dr. Waagen has suggested the similarity of this peculiar ligulate process to 
the visceral tube occurring in many forms of Athyris, but it is evident from its 
* Bulletin Cornell University, vol. i, No. 2, pp. 5, 6. 1874. 
t Salt-Range Fossils; Brachiopoda, p. 486. 1883. 
