DESCRIPTION OF CERTAIN CRUSTACEA, BROUGHT HOME BY THE 
U.S. N. ASTRONOMICAL EXPEDITION. 
BY CHARLES GIRARD. 
The Crustacea collected are but few, and of the Decapod division: some Brachyura, an Ano- 
moura, and a Macroura, constitute the entire list. 
The latter two, Aglea and Rhynchocinetes, constitute, each in itself, a natural group; both 
their structural peculiarities, and the deep interest which their history consequently involves, 
have suggested the following detailed descriptions of these two types. 
DECAPODA ANOMOURA. 
CENOBITIDZA AGLEID&A, 
Genus AXGLEA, Leach. 
Gen. cuar. Carapax depressed, longer than broad, anteriorly tapering, dilated upon the 
branchial region, diminishing in width posteriorly, and biarticulated. Frontal region armed 
with an acute rostrum. External antenne about the length of the carapax. External maxil- 
laries pediform. Posterior segment of the thorax movable. Legs of moderate size. Abdom- 
inal region shorter than the thoracic; broad, reflexed inferiorly and anteriorly, composed of 
six or seven segments, five of them bearing oviferic legs. 
Syn. Aiglea, Lracu. Dict. Sc. Nat. XVIII, 1850, 29. 
Oxs. At the time this genus was instituted, there was but one species known, A. levis, an 
inhabitant of the coast of Chile. Recent investigations have brought to light a second, from 
the same litoral, and to-day we add a third to the list, inhabiting the fresh waters of the 
mountainous regions of the Chilean republic, not knowing, however, whether it is altogether 
peculiar to that geographic range. 
A great deal remains to be done in order to ascertain whether these species are really distinct 
from one another. In the want of authentic specimens of both A. levis and A. denticulata, I 
was not prepared to remove all the doubts I had entertained in regard to their zoélogical simi- 
larities and dissemblances. With upwards of twenty-five specimens, including both sexes, of 
A, intermedia, before me, I have been compelled to avail myself, for their determination, of the 
writings of my predecessors in the field ; and this has been done with the most earnest desire 
to arrive at the truth on this subject. I candidly confess that had I had but one specimen and 
but one sex, I would have hesitated describing it as a new species. But since my materials 
were ample, and the specific characters hence drawn were found not to vary throughout the 
whole range of the specimens examined, I felt much less justified in calling them either A. levis 
or A. denticulata, than ascribing to them a new name. 
The description given below, it may be trusted, will enable my followers in the field, with 
the assistance of similar materials from the coast of Chile, to determine the true zodlogical 
