CONCHIFERA. 739 
the genus Hippurites (placed by LAMARCK amongst the Cephalopoda) 
should be united (Ann. des Se. nat. v. 1825, p. 205, xv. pp. 258— 
266) seem, when the genera Crania and Calceola, belonging to the 
Lrachiopoda have been separated from them, to be allied to the 
Chamacea; they had probably, however, an entirely open mantle, 
like the theriacea, Ostreacea &c. (DesHayves Lncycl. méth., Vers. 
ur. p. 918). The Hippurites, large, elongate, conical shells, resem- 
bling in some degree, as to external form, the horns of mammals, 
were first discovered at the foot of the Pyrenees by Picor La 
Pryrovuse. Goxpruss, however, and D’Orsieny also, is of opinion 
that these Rudiste belong to the Brachiopoda aud by no means 
to the Lamellibranchiata (Ann. des Se. nat., sec. Série, xvi. 1842, 
pp. 173—192), in which they now find many supporters. 
Genera: Hippurites Lam., Caprina D’Orxgtexy, Spherulites 
Desmout. (and Radiolites Lamu.) Desu. (Birostrites Lam. a fictitious 
genus from the internal mould of Spherulites.) 
Comp. DESHAYES in Lamarck Hist. nat. des Ani. s. vert., 2e éd. VII. 
1836, pp. 278—292, Picot Dr La PreyrouseE De novis quibusd. Orthocera- 
titum et Ostracitum specieb. Norimb. 1781, fol.; DESHAYES Lssai sur les 
Sphérulites (Bullet. dela Soc. d’ Hist. nat. de Bordeaua, 1. 1827); O. ROLLAND 
Dv Roguan, Description des coquilles fossiles de la famille des Rudistes, qui 
se trouvent dans le terrain crétacé de Corbiéres. Avec planches. Carcassone, 
1841, 4to. 
Family XI. Zridacnacea. Mantle with lobes for the greatest 
part concrete in the margin, furnished with a superior aperture for 
the passage of foot, and two small inferior, the anterior anal, the 
posterior respiratory. Four tentacles round the mouth elongate, 
acuminate. Foot thick. Ligament external, narrow. Two adduc- 
tor muscles approximate or confluent; muscular impression single, 
little distinct. Sheli regular, equivalve, free. 
Cuvier (Réegne Anim. u. 1817, p. 475) remarked that in the 
conchifers of this family there is only a single adductor muscle. 
Consequently Lamarck placed the genus Z’ridacna subsequently in 
the division of the Monomyaria, with which, however, it does not 
agree. From the figures of the animal of Z’ridacna mutica given 
by Quoy and Garmarp in the narrative of the voyage of the Astro- 
labe (copied in Ouv. R. Ani., éd. il., Moll. Pl. 96, fig. 3). it seems 
that two muscles are present however, which lie close together, and, 
although in other species they are confluent and form a single 
muscle, this is no reason for separating 7ridacna from those families 
with which in other respects this genus has most agreement. 
47—2 
