TRIDACKA. 295 



of Lamarck. The trachelipodoua moUusca are described asliaving 

 the posterior part of the body spirally twisted and separated 

 from the foot ; always enveloped in a shell. The foot is free, 

 flat, attached to the base of the neck. Shell spiral, and enclosing 

 the animal when at rest. This order contains the families, Coli- 

 macea, Lymnacea, Melaniana, Peristomiana, Neritacea, Janthi- 

 nea, Macrostomata, Scalariana, Plicacea, Canalifera, Alata, 

 Purpurifera, ColumeUaria, Convolntge. The genera belonging to 

 these families, are represented in the plates, fig. 264 to 462. 



TEANSVEESE. (Crosswise.) A shell is said to be transverse, 

 when its width is greater than its length, that is, when it is 

 longer from one side to the other than from, the umbones to the 

 ventral margins. The term is applied by some anthors to express 

 the direction of the lines of growth in bivalve shells, and the 

 spiral lines in spiral shells. See Cokcekteic. 



TEAPEZIUM. Meg. Ctpeicardia, Lam. 



TEAPEZIPOEM, or 



TEAPEZIOD. (rpaTTE^ioy, trapesion, trapezium : eidog, eidos 

 form.) Having four unequal and unparallel sides. Ex. Cucullsea, 

 fig. 133. 



TRIBULUS. Klein. Etcinula, Lam. 



TEICHOTEOPIS. Brod. and Sow. (Tpixoe, trichos, hair ; rpoTrte, 

 tropis, keel.) Fam. Purpurifera, Lam. — Deser. Turbinated, 

 keeled, thin, umbilieated ; aperture longer than the spire ; entire ; 

 columella obliquely truncated ; outer lip thin, sharp ; epidermis 

 horny, produced into long hairs at the angles of the shell ; oper- 

 culum homy, with the nucleus lateral. — Obs. Although the 

 shells of this genus have. something of the shape of Turbo, they 

 are distinguished from that genus at once by the thinness of the 

 sheU. They are also known from Buccinium, by the absence of 

 a canal. Only two or three species are known, which belong to 

 the Northern and Arctic Oceans. T. bicarinata. PI. xx. fig. 

 429. 



TEIDACNA. Auct. Fam. Tridacnacea, Lam. Chamacea, Bl. — 

 JDescr. Equivalve, regular, inequilateral, radiately ribbed, adorned 

 on the ribs with vaulted foliations, waved at the margins, with a 



