BRACHIOPODA. . 121 



structure of the hinge-plate and of the urabonal 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 Adrimi and Acambona Osagensis, though not so highly developed as in the 

 first of these. This structure is of so frail a nature r^ 



that it is difficult to preserve it in prepared inte- ikj 



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- outime pronie o/"™«. i.f<»-mom-, Mar- 

 rately described by Derby* from the interiors of 7^\::'l^:it:TrZ'\:TeZ 

 Eumetria pmctulifera {= Hustedia Mormoni) obtained TllTJZlm.'ZT"T) '° 

 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 Terebraiula 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 Athyrib, but it is evident from its 



* Bulledn Cornell Univereity, vol. i, No. 2, pp. 5, 6. 1874. 

 t Salt^Range Foesils ; Brachiopoda, p. 486. 1883. 



