DEN 



L 129] 



DEN 



Owen. The name Dendrodus, 

 appears to have been supplanted by 

 that of Cricodus. The Dendrodus 

 is an icthyolite of the old red sand- 

 stone, of which six species have 

 been particularized by Agassiz. 



DE'NDKOITE. A fossil resembling the 

 branch of a tree. 



DE'NDEOLITE. (from Sevtyov and 

 \i0os, Gr.) Fossil wood; the 

 fossil branch of a tree. 



DE'NSITT. (densitas, Lat. densitt, Fr. 

 densitd,, It.) Closeness; compact- 

 ness ; that property directly oppo- 

 site to rarity, whereby bodies con- 

 tain such a "quantity of matter in 

 such a bulk. The densities of 

 bodies are proportional to their 

 masses, divided by their volumes. 

 Hence if the sun and planets be 

 assumed to be spheres, their volumes 

 will be as the cubes of their diame- 

 ters. The strata of the terrestrial 

 spheroid are not only concentric 

 and elliptical, but the lunar in- 

 equalities show that they increase 

 in density from the surface of the 

 earth to its centre. 



The absolute density of, or the 

 quantity of matter contained in, 

 the earth, compared with an equal 

 bulk of any known substance, may 

 be nearly determined by the attrac- 

 tive force which any given mass of 

 matter exerts upon a plummet, when 

 suspended in its vicinity, to draw 

 it from a vertical line. By this 

 method it has been found that the 

 mean densisty of the earth is about 

 five times greater than that of water, 

 or nearly twice the average density 

 of the rocks and stones on the sur- 

 face. The mean density of the 

 ocean is only about one-fifth part 

 of the mean density of the earth. 

 More recent observations, by the 

 astronomer royal, on the pendulum 

 at the surface and at the bottom 

 of deep mines, give a mean of 

 6-809 for the earth's specific 

 gravity, while those made by the 



ordnance survey, on the deflection 

 of the plumb-line, give it as 5'14. 

 DE'NTAL. | (from dens, Lat.) A 

 DENTA'LITTM. ) shell-fish belonging, 

 according to Linnaeus, to the class 

 Vermes, order Testaca. The shell 

 consists of one tubulous arcuated 

 cone, open at both ends. There 

 are many species, distinguished by 

 the angles, striae, &o., of their shells. 

 The observations of Deshayes 

 lead to the conclusion that the 

 genus Dentalium approaches very 

 closely to the molluscs, if, indeed, 

 it does not belong to them. 

 The dentalia are found in deep 

 water, frequently near the shore, 

 inhabiting the ocean only; they 

 are solitary. Captain Yidal drew 

 up dentalia from the mud of 

 Galway Bay from a depth of 240 

 fathoms. The animal is a terebella. 

 The shells are known commonly 

 by the name of tooth-shells, or 

 sea teeth. Twenty-two species 

 have been described, seven of 

 which inhabit our coasts. 

 DE'NTALITE. ] (from dens, a tooth, 

 DE'KTALITHE. ) and \iOos, a stone.) 

 A fossil dentalium found in the 

 tertiary formations, in the gait and 

 in the lower green sand. Of these 

 there are many species ; as the Den- 

 talium planum, D. striatum, D. el- 

 lipticum, D. decussatum, &c. See 

 Ditrupa. 



DENTA'TA. A name given to the 

 second vertebra of the spinal 

 column, from a tooth-like process 

 which it possesses. 



DE'NTATE. } (dentatus, Lat.) Indent- 

 DE'NTATED. ) ed; jagged; notched; 

 toothed. In botany, leaves are 

 called dentated, when the border 

 is beset with horizontal projecting 

 points or teeth, with rather a 

 distant space between each, and of 

 the same consistence as the sub- 

 stance of the leaf itself : applied 

 also to stipules having spreading 

 teeth about the margin, remote 

 from each other. 



