372 



MANUAL OF THE MOLLTJSCA. 



Shell imiDunctate,* transversely oyal or elongated, tri-lol)ed, 

 beaked, bi-conyex, mtii a dorsal ridge and yentral furrow ; 

 hinge-line wide and straight ; area moderate, striated across ; 

 foramen angular, open in the young, afterwards progressively 



Dorsal valve. 



Fio\ 18?. 



Ventral valve. 



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

 muscular scar, consisting of the single adductor flanked by two 

 cardinal impressions ; dorsal valve with a small cardinal process, 

 a divided hinge-plate, and two conical sj)ires directed outwards 

 and nearly filling the cavity of the shell ; crura united by an 

 oral loop. The shell and spires are sometimes silicified in lime- 

 stone, and may be developed by means of acid. In S. mosqiiensis 

 the dental plates are prolonged nearly to the front of the ventral 

 valve. 



Bistrihution, 220 species. Lower Siluiian — Trias. Arctic 

 America — Chili, Falkland Islands, Europe, China, Thibet, 

 Australia, Tasmania. In China these and other fossils are used 

 as medicine. 



Sub-genera. Spiriferina, D'Orbigny. S. Walcotti, PI. XV., 

 Pig. 14. Sliell punctate, external surface spinulose ; foramen 

 covered by a pseudo-deltidium ; interior of ventral valve with a 

 prominent septum, rising from, the adductor scar. Distrihution, 

 29 species. Carb. — Lower Oolites. Britain, France, Germany, 

 South America. 



Oyrtia, Dalman. C. exj)orrecta, PI. XY., Fig. 15. Shell 

 impunctate, pyramidal, beak prominent, area equiangular, 

 deltidium with a small tubular foramen. Fossil, 10 species. 

 Silurian — Trias. Europe. In C. hicchH, heferoclyta, calceola, 

 &c., the shell is punctate. 



Suessia (imbricata), Eudes Deslongchamps, 1855. (Dedicated 

 to M. Suess). Shell like Spirifera ; texture fibrous; hinge area 

 wide as the shell ; foramen deltoid ; large valve with two 

 cardinal septa, and a prominent central septum, supporting a 

 little plate ; small valve with a tri-lobed cardinal process, and 



* Professor King attributes this to metamorpliism ; 5. Demnr/u, Bouch., from (he 

 Devoman limestone, is punctate. (Carpenter.) 



