264 



SPONDYLUS. 



— Obs. This genus, which is only known in a fossil state, is 

 distinguished from Terebratula externally, by the flat area in one 

 valve, internally, by the singular spiral process from which the 

 above name is derived. Fig. 214, 215. Most of the species be- 

 long to the mountain or carboniferous limestone. 



SPIROGLYPHUS. Daud. A genus consisting of a species of 

 Serpula Auct. which makes a groove for itself in the surface of 

 shells. Serpula spirorbis, var. Dillwyn. Fig. 8. 



SPIROLINA. Lam. A genus of microscopic Foraminifera. 



SPIROLOCULINA. D'Orb. A genus of microscopic Foraminifera. 



SPIRORBIS. Lam. A genus composed of species of Serpula, 

 Auct. which are coiled round in a spiral disc like a snake at rest. 

 S. nautiloides, fig. 5, is the common little white shell, found upon 

 the shell of lobsters. 



SPIRULA. (Spira, a winding compass.) Fam. Lituolata, Lam. 

 Lituacea, Bl. — Descr. Convolute, smooth, symmetrical, discoid, 

 with parallel unconnected whorls, divided into numerous cham- 

 bers by transverse septa ; siphon continuous. — Obs. This 

 pretty little shell is partly internal, only a part of it being visible 

 when on the animal. Fig. 471. 



SPISULA. Gray. A genus composed of Mactra fragilis, and 

 other similar species, which have the ligament sub-external, mar- 

 ginal, not separate from the cartilage ; with the posterior lateral 

 teeth double in one valve, and single in the other. M. fragilis, 

 fig. 80, is the species figured for Spisula in Mr. Gray's paper on 

 the Mactradse, in the second series of Loudon's Magazine of 

 Natural History. "We have since learned, however, that it was 

 figured there by mistake, not having been intended for a Spisula, 

 but belonging more properly to the genus Mactra, as defined 

 by Mr. Gray, whose description of Spisula, is as follows : — 

 " Shell ovate, trigonal, sub-angular at each end. Hinge and 

 lateral teeth as in Mactra, but hinge of left tooth small. Sipho- 

 nal inflexion ovate.' ' The principal difference between Spisula 

 and Mactra is, that the ligament is not separated from the 

 cartilage in the former. 



SPONDYLUS. Auct. {A shell-fish, Ancients.) Fam. Pectenides, 



