CONCHIFERA. 727 



xrv. PI. 2022, 23, figa. i, 2. In the mount of St Peter is found Ostrca 

 larva of which the elongated crooked shell with folded margins has some 

 resemblance to the larva of an insect. 



In some species the inferior shell, when the individuals are older, is 

 curved upwards at the point and very thick. Of these LAMARCK formed 

 his genus Gryphcea. (Sp. Gryphcea angulata LAM. from the coast of Peru.) 

 These forms in the fossil state especially abound in the Oolite and Lias 

 formations (as Gryphcea arcuata LAM., BLAINV. Malac. PL 59, fig. 4, 

 BRONN Lethcea, Tab. 19, figs, i a, I}; hence the name Gryphite-limestone, 

 in geological works. In Exogyra SAY, Sow. the point is not bent upwards, 

 but sideways. Species of this form occur especially in the chalk- formations. 



Family III. Pectinidea. Mantle open with margin thick, 

 tentaculate, often ocelliferous. Foot small. Shell regular or sub- 

 regular, solid, often marked by longitudinal ribs, mostly auriculate. 



Spondylus L. Shell inequivalve, adherent, mostly auriculate, 

 rude or muricate. Hinge with two strong teeth in each valve and 

 pit of ligament intermediate. Animal (Argus POLI) with body 

 compressed and margin of mantle cirrate and ocelliferous. Foot 

 small, disciform, supplied with a middle cylindrical filament sus- 

 taining an oval capitulum. Adductor muscle very large, central. 



Sub-genus : Plicatula LAM. Shell inauriculate, plicate ; inferior 

 valve without external cardinal area. 



Sp. Spondylus plicatus L., Plicatula ramosa LAM., CHEMN. Conchyl. Tab. 

 47, figs. 479, 480; Plicatula, cristata LAM., BLAINV. Malac. PL 62, fig. 2, 

 GUERIN Iconogr., Moll. PL 25, fig. 9, &c. There are also fossil species of 

 this form. 



Sub-genus : Spondylus LAM. Shell mostly auriculate. Inferior 

 valve produced beyond the hinge, area in superior trigonal, flat, 

 mostly divided by a median furrow. 



Sp. Spondylus Gcederopus L., POLI Test. utr. Sicil. n. Tab. 21, figs. 20, 21, 

 Tab. 22, Encycl. meth., Vers. PL 190, fig. i; in the Mediterranean; 

 Spondyl. americanus LAM., GUER. Iconogr., Moll. PL 25, fig. 8, &c. 



Fossil species of Spondylus are found in the chalk-formation. To Spon- 

 dylus, moreover, some fossil genera, whose characters are of no sufficient 

 value,, are referred by DESHAYES, as Podopsis LAM., Pachytes DEFR., 

 Dianchora SOWERBY. Comp. Ann. des Sc. natur. xv. 1828, pp. 427 434, 

 and the second edition of LAMARCK Hist. not. des Ani. s. vertebr. vn. pp. 

 195198. 



Hinnites DEFR. Shell irregular, subovate or orbicular, auriculate, 

 affixed. Hinge edentulous, pit of ligament narrow, deeply cut 

 out. 



