259 



toothed. Fossil, 4 sp. Lias Pliocene. The recent Limaa ? Sarsii 

 (Loven) Norway (= L. crassa of the JEgean ?) has the mantle-border plain. 

 Some of the larger recent sp. have obscure lateral teeth. 



Distr. 20 sp. Norway, Brit. W. Indies, Canaries, India, Australia; 

 1 150 fms. The largest living sp. (L. excavata, Chemu.) is found on the 

 coast of Norway. 



Fossil, 200 sp. Garb. ? Trias . U. States, Europe, India. The so- 

 called Plagiostoma spinosum is a Spondylus. 



SPONDYLUS, (Pliny) L. Thorny-oyster. 



Type, S. gsedaropus, L. Ex. S. princeps, PL XVI. fig. 15. 



Si/n. Dianchora, Sby. Podopsis, Lam. Pachytes, Defr. 



Shell irregular, attached by the right valve, radiately ribbed, spiny or 

 foliaceous ; umbones remote, eared ; lower valve with a triangular hinge- 

 area, cartilage in a central groove, nearly or quite covered ; hinge of 2 curved 

 interlocking teeth in each valve ; adductor impression double. 



Animal, with the mantle open and gills separate, as in Pecten ; lips 

 foliaceous, palpi short ; foot small, cylindrical, truncated. 



In aged specimens the circular portion of the muscular scar exhibits den- 

 dritic vascular markings. The lower valve is always most spiny and least 

 coloured; in some sp. (like S. imperialis] the shell is scarcely, if at all, attached 

 by its beak or spines. The inner shell-layer is very distinct from the outer, 

 and always wanting in fossil specimens from calcarious rocks, then called 

 Dianchora. Specimens from the Miocene of St. Domingo, which have lost 

 this layer, contain a loose mould of the original interior. Water-cavities are 

 common in the inner layer, the border of the mantle having deposited shell 

 more rapidly than the umboual portion. ( Owen, Mag. Nat. Hist. 1 838, p. 409.) 



Distr. 30 sp. W. Indies, Canaries, Medit. India, Torres Straits, Pacific, 

 W. America: 105 fms. 



Fossil, 45 sp. Inf. Oolite ? Neocomian . Europe, U. States, India. 



Sub-genus, Pedum, Brug. P. spondyloides, PI. XVI. fig. 16. Shell 

 thin, smooth, compressed, attached by a byssus passing through a deep notch 

 in the right valve. Inhabits coral-reefs, where it is found half-imbeded :, 

 Red Sea, Indian Ocean, Mauritius, Chinese Seas. 



PLICATULA, Lamarck. 



Etym. Plicatus, plaited. 



Type, P. cristata, PL XVI. fig. 17. 



Shell irregular, attached by the umbo of the right valve ; valves smooth 

 or plaited ; hinge-area obscure ; cartilage quite internal ; hinge-teeth, 2 ID 

 each valve ; adductor scar simple. 



Distr. 6 sp. W. Indies, India, Philippines, Australia, W. America. 



Fossil, 40 sp. Trias . U. S. Europe, Algeria, India. 



P. Mantelli (Lea) Alabama, has the valves eared. 



