172 
CLASS CRUSTACEA. 
Pactolus, Leach , 
Have the four or six anterior feet simple, or without forceps ; 
the internal extremity of the penult articulation of the four 
hinder ones is prolonged into a tooth, forming with the last 
articulation a forceps or didactylous hand. The testa has the 
form of that of leptopodia, and the tail presents the same num- 
ber of segments, but the feet are much shorter ; those of the 
third pair are wanting in the individual which has served 
for the establishment of this section. {Pactolus Boscii , 
Leach.) 
Lithodes, Latr ., 
Pesemble, as to the form of the first eight pair of feet, the 
other trigona. Their length, however, appears to augment pro- 
gressively from the second to the fourth, but the last two are 
very small, folded, but little apparent, imperfect, and as it 
were, useless. The tail is membranaceous, with three crus- 
taceous and transverse spaces on the sides, and another at 
the end, representing the segmentary divisions. The eyes 
are approximate interiorly ; the external jaw-feet are elon- 
gated, and projecting ; the testa is triangular, very spiny, and 
terminated anteriorly in a denticulated point. These Crustacea 
are proper to the northern seas. [Cancer maia , Linn.) 
Our sixth section, that of Cryptopoda, is composed of 
brachyurous Crustacea, singular in this, that the feet, with 
the exception of the two anterior, or claws, can be entirely 
withdrawn, and concealed, under an advancement, in the 
form of a vault, of the posterior extremities of their testa. 
This testa is almost semi-circular or triangular ; the upper 
blade of the forceps is more or less raised, and denticulated 
like a ridge. In the species in which those are largest, they 
cover the front of the body. 
