SIPHON. ([Greek: Siphon], siphon.) A pipe, or tube. A shelly tube passing through the septa of chambered shells. It is said to be _dorsal_, _central_, or _ventral_, according to its situation near the outer, or inner parts of the whorl. See Introduction. SIPHONAL SCAR. The name applied by Mr. Gray, to the opening or winding sinus in the palleal impression of a bivalve shell, in the place where the siphonal tube of the animal passes. SIPHONARIA. Sow. ([Greek: Siphon], siphon.) _Fam._ Phyllidiana, Lam. Patelloidea, Bl.--_Descr._ Patelliform, depressed, inclining to oval, ribbed; apex nearly central, obliquely inclining towards the posterior margin; muscular impression partly encircling the central disc, but interrupted in front, where the head of the animal reposes, and at the side by a siphon, or canal passing from the apex to the margin.--_Obs._ This siphon, which is in some species very distinct, serves to distinguish this genus from Patella. S. Sipho, fig. 231*. SIPHONOBRANCHIATA. Bl. (_Siphon_, and _Branchiæ_, gills.) The first order of Paracephalophora Dioica, Bl. divided into the families Siphonostomata, Entomostomata, and Angiostomata. SIPHONOSTOMA. Guild. A sub-genus of Pupa, consisting of several elongated species, which have the aperture detached from the whorls; such as P. costata, and fasciata. SIPHONOSTOMATA. Bl. ([Greek: Siphon], _siphon_; [Greek: stoma], _stoma_, mouth.) The first family of Siphonobranchiata, Bl. the shells of which are extremely variable in form, but always have a canal or notch at the anterior extremity of the aperture. This family partly answers to the Canalifera of Lamarck and the genus Murex in the system of Linnæus. It contains the genera Pleurotoma, Rostellaria, Fusus, Pyrula, Fasciolaria, Turbinella, Columbella, Triton, Murex, Ranella, and Struthiolaria. SIPHUNCLE. (Siphunculus.) A small siphon. SISTRUM. Montf. RICINULA, Auct. fig. 413. SKENEA. _Flem._ A genus including some species of EUOMPHALUS and CIRRUS. SMILUM. Leach. _Fam._ Pedunculated Cirripedes.--_Descr._ Thirteen pieces, ten of which are in pairs, lateral, subtriangular; one posterior dorsal, linear; all smooth; peduncle hairy.--_Obs._ This genus is distinguished from Pentelasmis, by the number of its valves, and from Scalpellum, by the hairy peduncle. S. Peronii, fig. 36. SNAIL. The common garden Snail, so destructive to our vegetables, belongs to the genus Helix. The water snail, found in ponds, is Planorbis. SOL. Humph. A genus consisting of several species of the genus Trochus, and corresponding with the sub-genus Tubicanthus, Sw. Malac. Fig. 349.