- ^ *SEVAS y wm BRULEDIASVATEE 
From the American Journal of Science and Jrts, 9nd. Series, Vol. XIV.—July, 1852. 
[Abstract of a paper in the Proc. Acad. Nat. Sci, Philad., 1852. pp. 6-28.] 
3 
CONSPECTUS OF THE CRUSTACEA 
» 
OF THE 
*- 
EXPLORING EXPEDITION UNDER CAPT. C. WILKES, U. S. N. 
By JAMES. D. DANA. | b 
PAGURIDEA, continued, MEGALOPIDEA and MACROURA. 
Tnt genera of Paguridea described in this paper have already heen 
mentioned in this Journal.* "The following are the observations on the 
Megalopidea, together with the descriptions of the new genera, omitting 
those of the species. 
Mrcagas. 
'The question of the maturity or immaturity of the Megalope and 
that of their true place in the natural system, still remain in doubt. 
Without touching on these points, at this time, I propose to describe 
some new genera and species pertaining to the group. 
The species, however diverse, agree in the structure of the abdomen 
and its.caudal appendages ; in the position of the four antennz between 
the eyes; in the articulations of the outer antenne ; in the inner an- 
tennz folded longitudinally or obliquely either side of the beak ; in the 
general form of the outer maxillipeds; in the large size and lateral 
position of the eyes without orbits; in the general structure of the 
legs; and in their habits. 'The beak is either horizontal or flexed down- 
ward, and has usually a sharp prominent tooth, either side of it, exte- 
rior to the inner antennz. 
The genus Megalopa, Leach, as now accepted, embraces two dis- 
tinet sets of species—the JM. Montagui and armata for which it was 
instituted by Leach, and the M. mutica of Desmarest. 'T'he former (the 
true Megalopz) have the beak nearly horizontal, with rarely a tooth 
either side, and there is a reflexed spine on the ventral surface of the 
first joint of the 8 posterior legs. The latter has the beak bent down- 
ward vertically, and either side of it there is a prominent spine or tooth ; 
the ventral surface of the base of the legs is unarmed. 'T'he M. mutica 
is very closely related to Monolepis spinitarsus of Say,the only dif- 
ference being that the extremity of the posterior legs in this species of 
Monolepis bear 3 or 4 sete rather longer than the tarsus, while 
the descriptions of the mulca make mention of no such sete. "The 
posterior legs in Monolepis fold up and overlie the carapax: but 
€^ 
* Vol. xiii, p. 121. 
Sxcox» Sxgizs, Vol. XIV, No. 40.—July, 1852. . 15 
Ty eA 
