CONCHIFERA. 739 



the genus Hippurites (placed by LAMARCK amongst the Cephalopoda) 

 should be united (Ann. des Sc. nat. v. 1825, p. 205, xv. pp. 258 

 266) seem, when the genera Crania and Calceola, belonging to the 

 Brachiopoda have been separated from them, to be allied to the 

 Chamacea; they had probably, however, an entirely open mantle, 

 like the JZtheriacea, Ostreacea &c. (DESHAYES Encycl. meth., Vers. 

 in. 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 PICOT LA 

 PEYROUSE. GOLDFUSS, however, and D'ORBIGNY also, is of opinion 

 that these Rudistce belong to the Brachiopoda and by no means 

 to the Lamellibranchiata (Ann. des Sc. nat., sec. Serie, xvm. 1842, 

 pp. 173 192), in which they now find many supporters. 



Genera : Hippurites LAM., Caprina D'ORBIGNY, Sphcerulites 

 DESMOUL. (and Radiolites LAM.) DESK. (Birostrites LAM. a fictitious 

 genus from the internal mould of Sphcerulites.) 



Comp. DESHAYES in LAMABCK Hist. nat. des Ani. s. vert., ie 6d. vn. 

 1836, pp. 278 292, PICOT DE LA PEYKOUSE De novis quibusd. Orthocera- 

 titum et Ostracitum specieb. Norimb. 1781, fol. ; DESHAYES Essai sur les 

 Spherulites (Bullet, de la Soc. d'Hist. nat. de Bordeaux, i. 1827) ; O. HOLLAND 

 Du ROQUAN, Description des coquilles fossiles de la famille des Rudistes, qui 

 se trouvent dans le terrain cretace de Corbieres. Avec planches. Carcassone, 

 1841, 4to. 



Family XI. Tridacnacea. 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. Shell regular, equivalve, free. 



CUVIER (Regne Anim. n. 1817, p. 475) remarked that in the 

 conchifers of this family there is only a single adductor muscle. 

 Consequently LAMARCK placed the genus Tridacna subsequently in 

 the division of the Monomyaria, with which, however, it does not 

 agree. From the figures of the animal of Tridacna mutica given 

 by QUOY and GAIMARD in the narrative of the voyage of the Astro- 

 labe (copied in Cuv. R. Ani., ed. ill., Moll. PI. 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 Tridacna from those families 

 with which in other respects this genus has most agreement. 



472 



