CLASSIFICATION OF THE BRACHIOPODA. 67 



^ Section A. Trigonosemus. K(enig,\%2h} 



Type — T. elegans, Koenig. Int., PI. VI, figs. 15, 16. 



Tekebkatula (part), of Authors. 

 FissuEiROSTBA, If Ovbigny . 

 Delthykidea, M'Coy. 



Shell inequivalve, oval, transverse or elongated : dental valve always convex, smaller 

 one moderately so, flat or longitudinally depressed : beak produced, recurved and trun- 

 cated by a small foramen originating at the summit of the beak and extending on the 

 opposite side to the area. This last is large, margined and carinated exteriorly ; the delti- 

 dium occupying less than a third of the surface, a small portion only edging the foramen ; 

 external surface striated or variously costated : hinge articulating by the means of teeth 

 and sockets : between the socket ridges a remarkably large and produced cardinal process 

 or boss fills a cavity in the beak of the larger valve ; the loop is doubly attached ; first near 

 the base of the socket ridges and afterwards to a short mesial septum before becoming 

 reflected : the adductor muscular impressions are deeply indented on either side close to 

 the base of the septum. 



05s. The arrangements of the loop are very similar to those of Terehratella : the 

 greatest difierence resting in the form of the cardinal process, area, and position of the 

 foramen. This sub-section has in reality very little importance, and cannot I think claim 

 a generic rank. 



Geol. range. — Hitherto no species has been observed out of the cretaceous period. 



Examples : T. elegans, Koenig ; pulchellus, Nils., sp. ; incertus, Dav. ; pectiniformis, 

 Buch, sp. ; &c. 



"^Section B. Terebrirostra, D'Orb., 1847.^ 



Type—1. LYRA, Sow. Int., PI. VI, figs. 17, 18. 



Tebebratula (part), of the generality of Authors. 

 Trigonosemus (part), Koenig. 

 Terebrirostra, D'Orb., Be Ryckholt, &c. 

 Waldheimia (part). Gray (not King). 



Animal unknown. Shell more or less oval, inequivalve ; beak considerably elongated, 

 almost straight, with a false area and narrow deltidium : the extremity of the beak is 

 truncated by a circular foramen, partly margined by a deltidium ; valves articulating by the 

 means of teeth and sockets ; internal arrangements of the calcified supports of the arms 



1 Icones Fossilium Sectiles, 1825. 



2 Cons. Zool. et Geol. sur les Brach. — Comptes rendu de I'Acad. des Sciences, 1847; and Paleont. 

 Fran9. Ter. Cretaces, vol. iv, p. 126, 1847. 



