ORDER DECAPODA. 
165 
being withdrawn altogether within their cavities, and whose 
claws, in the males at least, are notably thicker than the 
other feet. 
Mithrax, Leacli . 
Their claws are very robust, with the fingers hollowed like 
a spoon at the end. The stem of the lateral antennae is sen- 
sibly shorter than the pedicle. The tail is composed of seven 
articulations in both sexes. ( Mithrax spinicinctus , Latr.) 
Acanthonyx, Latr., 
Have an advancement in the form of a tooth, or spine, at 
the inferior side of the legs. The under part of the tarsi is 
hairy, and, as it were, pectinated, and the upper part of the 
testa is even. The tail of the males presents, at most, six 
complete segments. {Meria glabra, Collect, du Mus. d’Hist. 
Nat.) 
Pisa, Leach, 
Whose claws are of a middle size, with the toes pointed. 
The legs have no spine underneath, and the tail consists of 
seven segments in both sexes. As well as in the preceding 
subgenera, the lateral antennae are inserted at an equal dis- 
tance from the fossets, which receive the intermediate, and 
from the ocular cavities, or more approximated to the latter. 
Some, as in the genus naxia of Dr. Leach, have two 
ranges of denticulations under the tarsi, others have but a 
single range of denticulations, or a simple fringe of thick 
hairs in a knob, under the same articulation. Those which 
are in this last case form the genus Lissa of the same. 
Among those which have but a single range of denticula- 
