66 J. D. Dana on the Classification of Mammals. 
real weight, are not, to rome zoologists, unquestionable or 
authoritative evidence on this point, 
But, while the structural distineticos mentioned may fail to 
establish Man's independent ordinal rank, there is a character- 
istic that appears to be decisive,—one, which has that deep found- 
Sh in zoological science required to give it prominence and 
authori 
The eeabicts referred to is this:—that while all other Mam- 
—~ of the eae and abbreviation of sts posterior portion 18 & 
of elevation; but further than os; that the transfer of tlhe 
mitensbe members of the thorax to the cephailic series is the foundation 
of rank among the orders of Crustaceans. In the highest order 
of this class—that of the Decapods, (containing crabs, lobsters, 
shrimps, ete.), nine pairs of organs, out of the fourteen pertaining 
to the head and thorax, belong to the head—that is, to the senses 
and the mouth. In the second order, — of the pow 
there are only seven pairs of organs, out of the fourteen, thus 
devoted to the Aare, —two of the pairs which are mouth-organs 
in the Decapods being true legs in the Tetradecapods. In the 
third or lowest order, that of the Entomostracans, there are only 
six, five, or four pairs of cephalic organs; and besides, these, in 
most species, are aghe pediform rm, even the mandibles — 
namely, (8) that a decline in grade, after the laxness and elonga- 
tion o the anterior and terior extremities have reached theif 
limit, is further exhibited by a degradation of the body and espe 
ale of its extremities. 
on Classification, page 1395 ; also this 
his Report on Crustacea, the 
1 lained in this paper are 
Soleus, vol. xxii, . 14, 1856; where aires es exp) oer ae Rie oo 
illustrated by many examples, and with direct reference 
classification. 
