72 Review of O. Gregory’s Treatise on Mechanics. 
Cabinets of the Lyceum and Dr. Mitchill. 
Length exclusive of the margin 2.6 Breadth 1.0 
Length including the margin 3.0 Breadth 2.2 
Shell oblong oval, coated with a coarse, green, rough 
epidermis, closely adhering to the shell, and concealing the 
whole, except a small part of the carinated center of the 
back, in which the shell appears black, smooth and shin- 
ing ; colour, under the epidermis and on the inside, pure 
ivory white; margin more than half as broad as the shell, 
thickly studded with unequal, irregular, white, round head- 
ed spines. se ger pale green : inner margin lighter colour 
than the animal. 
Remarks. | 
The spines are white, in the specimen figured, or white 
with a black center: but the native colour is black or dark 
amethystine, and the white is a calcarious accretion, which 
appears to be a microscopick Cellepore. 
ew-York, March 3, 1823. 
< * 
MATHEMATICS. 
elite 
. 
Anr. X.—A Treatise of Mechanics, theoretical, practical’ 
and descriptive: by Ovintaus Grecory, LL. D.—3 
vols. 8vo. London, 1815. 
(Communicated.) 
The science of mechanics, whether considered in its the- 
ory as a subject of curious and refined speculations, caleu- 
lated for the learned, ingenious, and contemplative, or in 
practice as contributing to the conveniences and elegancies 
of life, and the wealth of nations, may be ranked the first 
and most important of all human acquirements. What 
ord Bacon says of all true philosophy, is eminently appli- 
cable to this branch of it, * that it enlarges the powers of 
man, and extends his dominion in nature.” By it, her 
most refractory and opposing powers have been subdued, 
