CARBON I I'KROUS AGE. 17 



(i.nus S1MKIFER, SOWERBY. 



Sy*o*. Ifyitrroliln, Anomitrt and Terrl,rntulilti (part) of early author*. 



/ .'.r<i/u/,i (part), LAMAK. K, I'rodr. 1799, 85 (not of author* generally). 



r./rr, SUWKUHT, Miii. Conch. II, 1815, 42. 

 Triyooir,t:,, K.KMO, loon. Beet. No. 70, 1825. Bmoxx, Llh. Qeog. 1837, 77. KMO (put), Monog. 



IVrui. FOHH. Kuglaud, Is.'.o, 11;,;. 



f 'A..ri.</i'fr*, KIHCUER, Prodr. nr le Chorii-tites tloto. 1825, xx. 

 /'.//Ayr". DALXAH, Kongl. Vet. Ac. Handl. 1827. 



i, D ALMAS, ib., 1827. 



>>//-i/rr.i, SOWIBBT, Ind. to Min. Con. 1825 ; and of several later author*. 

 'ii'.i, McCor, Synop. Carb. FOM. Ireland, 1844, 139. 

 /ri (part), McCoi, ib., 142. 



Itrackjtkyru, Mct'oT, Ib., 144. 



Ambocalia, HALL, Thirteenth An. Rept. Regents Unirenlty of N. Y., 1860, 71. 

 t'tymol. Spira, a spire ; frro, to bear. 



Type. Sjiiri/er cutjiiilatui, SOWE 



Shell more or less triangular, semicircnkr, transversely elongate, or subglobosc, 

 with or without a mesial fold and sinus; lateral margins rounded, angular, or 

 sometimes produced into mucronatc, wing-like extensions ; structure impunctate ; 

 surface plicate, costute, striate or smooth sometimes roughened by minute 

 granular or spinous projections. Cardinal line straight, as long as, or shorter 

 than, the greatest transverse diameter of the valves. Hinge articulated by short 

 teeth and sockets, and provided with a more or less developed cardinal area in 

 each valve ; that of the ventral valve being larger than the other, flat or arc-lied, 

 and generally inclined back over the hinge divided by a triangular foramen 

 usually more or less (sometimes entirely) closed by a false deltidium, which is 

 occasionally pierced by a small circular or oval aperture near the beak ; area of 

 dor>al or smaller valve narrow, often linear, divided in the middle by a wide open 

 fi-Mire which is partly or entirely occupied by the cardinal muscular process. 

 Beak of ventral or larger valve more prominent than that of the other, incurved or 

 more or less nearly straight, that of the smaller valve short, and nearly always 

 incurved, 



In the interior of the dorsal valve the large spiral supports of the labial arms are 

 attached by their crura to the hinge plates, some distance from which they are 

 nearly or quite connected by a small process extending inwards from each. The 

 cardinal muscles seem to have been attached to the cardinal process, under, and in 

 front of which, the four large scars of the adductor muscles occur. In the larger 

 or ventral valve the cardinal teeth are placed one on each side, and at the base of 

 the foramen, and fit into corresponding sockets in the other valve; beneath the 

 hinge these teeth are supported by the strong dental lamina*, which vary much in 

 size and form, according to the species, and arc supposed to have received on their 

 inner sides the muscles of the peduncle. A considerable portion of the central 

 region of this \nl\e is occupied by the muscular MtM, which are generally divided 

 by a mesial ridge. Immediately on each side of this ridge occur the small longi- 



3 March, 1864. 



