oie MANUAL OF THE MOLLUSCA. 
Shell impunctate,* transversely oval or elongated, tri-lobed, 
beaked, bi-convyex, with 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. Fig. 168. Ventral valve. 
closed; ventral valve with prominent hinge-teeth, and a centrai 
muscular scar, consisting of the single adductor flanked by two 
cardinal impressions ; dersal 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 sometimes silicified in lime- 
stone, and may be developed by meansof acid. In S. mosquensis 
the dental plates are prolonged nearly to the front of the ventral 
valve. 
Distribution, 220 species. Lower Silurian—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. 8S. Walcoitti, Pl. XY., 
Fig. 14. Shell punctate, external surface spinulose; foramen 
covered by a pseudo-deltidium ; interior of ventral valve with a 
prominent septum, rising from the adductor scar. Distribution, 
29 species. Carb.—Lower Oolites. Britain, France, Germany, 
South America. 
Cyrtia, Dalman. OC. exporrecta, Pl. XV., Fig. 15. Shell 
impunctate, pyramidal, beak prominent, area equiangular, 
deltidium with a small tubular foramen. Jossil, 10 species. 
Silurian—Trias. Europe. In C. buchii, heteroclyta, 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 metamorphism; §. Demarlii, Bouch., from the 
Devonian limestone, is punctate. (Carpenter.) 
