D O L 



DOW 



dodo," as Dr.Mantell observes, "has been 

 annihilated, and become a denizen of the 

 fossil kingdom, almost before our eyes. 

 The bones of the dodo have been found in 

 a tufaceous deposit, beneath a bed of 

 lava, in the Isle of France ; so that if the 

 very few remains of the recent bird, 

 above alluded to, had not been preserved, 

 these fossil relics would have constituted 

 the only record that such a creature had 

 ever existed on our planet.'' Neverthe- 

 less, two centuries since, the dodo formed 

 the principal food of the inhabitants of 

 the isle of France. 



DOLABE'LLA. A genus of univalvular mol- 

 luscs the known species of which are 

 found in the Indian ocean and in the 

 Mediterranean. They differ from Aply- 

 siae only in the position of their branchiae 

 and their surrounding envelope. 



DOLA'BRIFORM. (from dolabra and forma, 

 Lat.) Hatchet-shaped ; a term more 

 commonly applied to leaves, cylindrical 

 at the base and having the upper part 

 dilated, thick on one edge and cutting on 

 the other. 



DO'LERITE. A variety of trap-rock, or 

 greenstone, composed of augite and La- 

 brador-felspar. 



DO'LIUM. (dolium, Lat. a tub, a tun.) A 

 subglobular ventrose univalve, spirally 

 ribbed in the direction of the whorls ; 

 the inferior whorl ample and ventricose ; 

 outer lip crenated, or dentated, through- 

 out its whole length. Aperture oblong, 

 ample, and notched ; epidermis light and 

 horny. Parkinson states that the dolium 

 has not been found fossil : this is not the 

 case ; one species, Dolium nodosum, has 

 been found at Clayton, near Hurst, in 

 Sussex, by R. Weekes, Esq. of Hurst. 



DO'LOMITE. A variety, or modification, of 

 limestone, consisting of magnesian earth 

 48 parts, and calcareous earth 52 parts. 

 It derives its name from Dolomieu, a 

 French geologist. There are three sub- 

 species. Von Buch maintains that lime- 

 stone has been converted into dolomite 

 by its proximity to porphyry in fusion, 

 and that the magnesia has been trans- 

 ferred from magnesian minerals in the 

 porphyry to the limestone ; the magnesia 

 being reduced to vapour or gas. Bake- 

 well. 



The name Zechstein (from zeche and 

 stein, Germ.) has also been given to dolo- 

 mite or magnesian limestone. This is a 

 calcareous deposit, of a somewhat variable 

 aspect ; it is fossiliferous. The zechstein 

 has not yet afforded any remains of trilo- 

 bites. It does not appear to be a deposit 

 widely spread over the European area. 

 As yet, it is principally known in Ger- 

 many and England. Dolomite is gene- 

 rally of a light fawn or yellow colour, and 



in some parts of a crystalline, in others of 

 a concretionary, character. It is included 

 in the new red sandstone group, its posi- 

 tion being immediately above the coal 

 measures. It is frequently traversed by 

 veins of carbonate of lime, and there are 

 sometimes met with enclosed in it hollow 

 geodes of calcareous spar, with sulphate 

 of strontian and sulphate of barytes. 



DO'LOMITE MA'RBLE. A variety of dolo- 

 mite of a white colour, occurring in small 

 granular concretions ; these concretions 

 are frequently so loosely united as to fall 

 apart by the slightest pressure. 



DOLOMI'TIC. Containing dolomite ; of the 

 nature of dolomite. 



DO'MITE. A variety of trachyte, and thus 

 named from being found in the Puy de 

 Dome, in Auvergne, in France. It has 

 the appearance and gritty feel of sandy 

 chalk. 



DO'NAX. (donax, Lat. S6va%, Gr.) Ani- 

 mal a tethys ; an equivalved inequilateral 

 bivalve, with a crenulate margin, the 

 frontal margin obtuse ; hinge with two 

 cardinal teeth in one valve, one in the 

 other ; the lateral teeth one or two, rather 

 distant. The shells of this genus are in 

 general triangular, inequilateral, flattened, 

 truncated before, and wedge-shaped. It 

 is found in sands and sandy mud, at 

 depths varying to ten fathoms. Nine- 

 teen species have been described, six of 

 which have been found in our seas. Se- 

 veral fossil species occur in the neigh- 

 bourhood of Paris. 



DO'RIS. In the Linnsean arrangement, a 

 genus of gasteropoda, belonging to the 

 class Mollusca. An animal inhabiting a 

 shell ; body, creeping, oblong, and flat 

 beneath ; mouth below, on the fore part ; 

 vent behind, on the dorsum, surrounded 

 by a fringe ; feelers two and four, retrac- 

 tile, and placed on the front of the upper 

 part of the body. They are all marine, 

 and are found in every sea. In Cuvier's 

 arrangement doris is placed in the order 

 Nudibranchiata. 



DO'RSAL. (dorsal, Fr. dorsale, It. from 

 dorsum, Lat.) Appertaining to the back, 

 as the dorsal fin, the dorsal ligaments, &c. 



DO'RSUM. (dorsum,Ltat.) The back : the 

 ridge of a hill is sometimes called the 

 dorsum. In conchology, it generally 

 means the upper surface of the body of 

 the shell, when laid upon the aperture or 

 opening. In the genera of patella and 

 haliotis, the dorsum means the upper con- 

 vex surface. 



DOWN. 



1. The fine soft under feathers of many 

 birds, as the swan, goose, Sac. 



2. The pubescence of plants, or very 

 soft, short hairs, covering various parts 

 of plants. 



