BRACH10PODA. 



223 



are sometimes spinulose, indicating the existence of rigid cirri, especially on 

 the front of the whirls ; valves articulated by teeth and sockets. 



Fig. 132. Dorsal; Ventral valve. % 



SPIRIFERA, Sowerby. 



Type, S. striata, Sby. fig. 132. Syn. Trigonotreta, Ko'nig. Choristites. 

 Fischer. Delthyris, Dalman. Martinia &c. M'Coy. 



Shell impunctate,* transversely oval or elongated, tri-lobed, beaked, bi- 

 convex, with a dorsal ridge and ventral furrow ; hinge-line wide and straight ; 

 area moderate, striated across ; foramen angular, open in the young, after- 

 wards progressively closed ; ventral valve with prominent hinge-teeth, and a 

 central muscular scar, consisting of the single adductor flanked by two cardi- 

 nal impressions : dorsal valve with a small cardinal process, a divided hinge- 

 plate, and two conical spires directed outwards and nearly filling the cavity 

 of the shell ; crura united by an oral loop. The shell and spires are some- 

 times silicified, in limestone, and may be developed by means of acid. In 

 S. mosquensis the dental plates are prolonged nearly to the front of the 

 ventral valve. 



Distr. 200 sp. L. Sil. Trias. Arctic America Chile, Falkland Ids, 

 Europe ; China ; Thibet ; Australia ; Tasmania. In China these and other 

 fossils are used as medicine. 



Sub-genera. Spiriferina, D'Orb. S. Walcotti, PI. 15, f.14. Shell punc- 

 tate, external surface spinulose ; foramen covered by a pseudo-deltidium ; in- 

 terior of ventral valve with a prominent septum, rising from the adductor 

 scar. Distr. 6 sp. Trias L. Oolites. Brit. France, Germany, S. America. 



Cyrtia, Dalman. C. exporrecta, PL XV. fig. 15. Shell impunctate, pyra- 

 midal, beak prominent, area equiangular, deltidium with a small tubular 

 foramen. Fossil, 7 sp. Silur. Trias. Europe. In C. BucUi, heteroclyta, 

 calceola, &c. the shell is punctate. 



ATHYRIS, M'Coy. 



Etym, A, without, thuris, a door.f (i. e. deltidium). 

 Syn. Spirigera, D'Orb. Cleiothyris, King (not Phil.) 



* Prof. King attributes this to metamorphism ; S. Demarlii. Bouch. from the 

 Devonian limestone, is punctate. (Carpenter). 



t Sometimes employed, incorrectly, in the sense of a door -way or foramen. 



