136 DELPHINULA. 



DACTYLUS. Humph. Marginella, Auct. 



DARACIA. Gray. A subgenus of Pyrgoma, including a species 

 which is remarkable for the irregularity of its form. It grows 

 upon a species of Monticularia, and the margin takes the shape 

 of the lobes by which it is surrounded. The aperture is large, 

 and completely closed by the operculum. Daracia (Pyrgoma) 

 Monticulariee, fig. 489, 490. 



DATE. A common name given to shells of the genus Pholas, on 

 account of their cylindrical form and consequent resemblance to 

 the fruit. For the same reason the name Pholas Dactylus has 

 been given by Naturalists to the species which we represent, fig. 66. 



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- 

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

 no shells. 



DECADOPECTEN. Ruppell. Pecten Plica, Linn. Fig. 172, 

 having a plicated hinge. 



DECOLLATED. (Decollari, 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 it 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- 

 late, fig. 289. 



DECUSSATED. Intersected by striae crossing each other. +Ex. 

 Rissoa, fig. 346. 



DELPHINULA. Montf. (Delphinus, a dolphin.) Fam. Scalariens, 

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

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

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



