SYMMETRICAL. 287 



SUBULATE. (Subula, an awl.) A term applied to shells which 

 are long and pointed aa in Terebra. Fig. 427, 428. 



SUBULINA. Beck, 1837. A genus founded on the high-spired 

 Helix octona, fig. 514. Macrospira, Guilding, 1840. 



SUCCINEA. Drap, (Succinum, amber.) Fam. Colimacea, Lam. 

 Limacinea, Bl. Sub-genus, Cochlohydra, Per. — Descr. Ovate, 

 rather elongated ; aperture large, entire, longitudinal ; spire 

 short; outer lip thin, continuous with the thin, sharp-edged 

 columella ; inner lip spread over a part of the body-whorl. — Obs. 

 The shells belonging to this genus of partly amphibious mollusca, 

 are distinguished from Linnsea by not having a fold on the colu- 

 mella. The S. amphibia is of a bright amber colour. PI. xiii. 

 fig. 265, 266. 



SULCATED. (SuLCATUS, lat.) Having grooves or furrows. 



SULCI. G-rooves or furrows. 



SUTURE. (Suiura, lat.) A seam, stitch, joining together. Ap- 

 plied particularly to the Hne which marks the' joining of the 

 whorls of the spire. The suture is distinguished as simple, as in 

 most cases ; or double, when accompanied by a parallel groove 

 close to it ; marginated, when produced into a ledge by the 

 matter which fills up and covers it ; obsolete, when it is fiUed up 

 so as not to be visible, as in the case of AnciUaria. 



SYCOTTPUS. Brown, 1756. A generic name applied to Pyrula 

 ficus, &c. 



STLVICOLA. Humph. Cyclostoma, Lam. 



STMMETE.ICAL. (o-w, syn, similar ; fxerov, metron, proportion.) 

 Both sides alike. Although the term is used thus as one of 

 distinction, it is to be observed that no shells are strictly and 

 perfectly symmetrical ; even in the Nautilus, the apex verges in 

 a slight degree towards one side of the shell. Two kinds of 

 univalve are symmetrical, or nearly so ; 1st. Those which are 

 symmetrically convolute, as the JSTautUacea and the Ammonacea, 

 which are spiral ; 2nd. Those which are not spiral, but simply 

 conical, as the patelliform shells. Bivalves belonging to the 

 Brachiopoda are also symmetrical. Ex. PateUa, fig. 229. Ammo- 

 nites, fig, 478. 



