BRACHIOPODA. 



333 



the hole at the extremity of the beak is round; the delti- 

 dium is single and very much lengthened ; the hinge teeth 

 are as usual ; a long apophysis springs from the hinge of 

 the smaller valve, and extends under the deltidium to the 

 other ; the inner scaffold is placed in the smaller valve on 

 a very conspicuous middle plate, and there is the rudiment 

 of a loop-shaped apparatus at the base of the hinge. — 

 Fossil. 



Only known in the chalk formation; the type is 

 T. Lyra. Sowerby illustrates this species in Mineral 

 Conchology, representing the beak lengthened out so much 

 that it is as long as the whole of the smaller valve, giving 

 the shell a singular appearance. 



Fissurirostra. D 'Orb. — Shell free, of a punctured 

 texture, oval or triangular ; the larger valve very convex, 

 with a flat broad triangular area, which extends from the 

 hinge to the extremity of the long projecting curved beak ; 

 the small valve is flat, or even concave ; the hole in the 

 beak has the form of a long slit, commencing at the point 

 of the beak ; the deltidium is triangular, and single ; the 

 hinge teeth are as usual ; the smallest valve has springing 

 from the beak, a very long horizontal apophysis which ex- 

 tends under the deltidium to the large valve ; the inner 

 scaffold is in the small valve placed on a projecting middle 

 plate ; traces may also be seen of a loop-shaped process at 

 the hinge ; in the middle of the valve an oval impression 

 appears on each side near the middle plate. The outer 

 surface is furnished with numerous dichotomous folds. 

 D'Orbigny conjectures that the opening at the beak is 

 closed in age. — Fossil. 



The species are only found at present in the chalk 

 formation. This genus and the preceding are by most 

 naturalists considered not distinct. 



