SIPHONOSTOMATA. 259 



sinuous. The muscular impression of the mantle, or palleal 

 impression of some bivalve shells, is sinuated near the posterior 

 muscular impression. 

 SINUS. (Sinus, a winding, or bay.) A winding or tortuous 

 excavation. The sinus in the outer lip of Strombus, fig. 406; and 

 that in the muscular impression of Venus, will be indicated by 

 the letter s. 

 SIPHON. (Bicpov, 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 open- 

 ing or winding sinus in the palleal impression of a bivalve 

 shell, in the place where the siphonal tube of the animal 



SIPHONARIA. Sow. (2i0ov, siphon.) Fam. Phyllidiana. 

 Lam. Patelloidea, Bl. — Bescr. 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 Branchia, 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 ; sucli as P. costata, and fasciata. 

 SIPHONOSTOMATA. Bl. (S^ov, siphon; aro^ia, 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 



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