Blainville gives the following characters of the animal 

 body oval subdepressed ; head subdivided in two equal 

 lobes ; tentacula and eyes indistinct; margin of the man- 

 tle crenulated and extending beyond a suborbicular foot as 

 in the Patellas, branchial cavity transverse, open a little 

 before the middle of the right side and provided in that 

 part with a fleshy lobe, of a square form, situated in the 

 sinus between the mantle and the foot ; retractor muscle 

 fjf the foot, divided into two parts, of which the posterior 

 is much the larger, arquated ; the other very small, before 

 the branchial orifice. 



Several species are known, attaching themselves to rocks 

 and other fixed bodies. 



SIPHONARIA ALTERNATA. 



DESCRIPTION. 



Shell conical, with more than thirty obsolete, hardly 

 elevated, unequal ribs: apex obliquely curved, the tip 

 pointing nearly in a parallel direction with the surface of 

 the shell, and acute : color brown, radiated with whitish : 

 hast nearly oval. 



SYNOKYM. 



Patella Alternata, Nob. Journ. Jlcad. Nat. Sc. 

 Vol. 5, p. 215. 



PI. ;38. 



