142 DEKDOSTREA. 



DEAD SHELL. A term used among collectors to signify that 

 the shell has been exposed on the sea-shore after the animal has 

 ceased to live. A shell in this condition is worn down by at- 

 trition, and loses its beauty and brilliancy of colouring by being 

 subject to the action of salt water. A dead shell may be known 

 by a certain hoary whiteness spread over its surface. 



DECACERA, Bl. The second family of the order Cryptodibran- 

 chita, Bl. containing the genera Calmar and Sepia, which have 

 no shells. 



DECADOPECTEN. Eiippell. Peoten Plica, Linn. Having 

 a plicated hinge. PL x. fig. 172. 



DECOLLATED. {Becollari, to be beheaded.) The apex or nu- 

 cleus of some shells being composed of a more fragile substance 

 than the rest, has a tendency to fall off. The reason of this pro- 

 bably is that the animal withdrawing from that part, leaves it 

 unprotected. "When the part falls off, the hole is stopped up by a 

 septum filling the cavity of the volution, so as to exclude the 

 air : the shell is then said to be decollated. Ex. Bulinus decol- 

 latus, fig. 289. 



DECUSSATED. Intersected by striae crossing each other. Ex. 

 Eissoa, fig. 346. 



DELPHIISTULA. Montf. (Belphinus, a dolphin.) Fam. Scala- 

 riens, Lam. Cricostomata, Bl. — Descr, Orbicular, depressed, 

 thick, rugose ; whorls few, angulated, branched at the angles ; 

 aperture pearly, rounded or sub-quadrate ; peritreme continuous, 

 thickened ; operculum horny, composed of numerous whorls. 

 — Obs. Several fossil species are found in the tertiary deposits. 

 D. laciniata. PI. xvi. fig. 352. Recent species belong to tro- 

 pical climates. 



DELTHTBIS. Dalman. Fam. Brachioponda, Lam. — Descr. 

 Hinge more or less rounded, with distant umbones ; both valves 

 convex ; with the umbo of the largest rostrated and deltoid, with 

 a hollow. This genus forms part of the genus Spirifer, Sow, D. 

 Plycotes, Dalman. PL xi. f. 205. 



DELTOID, (A, delta.) Triangular. 



DENDOSTREA. Swainson, (1840). (Aerdpoy, dendron, tree ; 



