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., 



Resemble, 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 inferiorly ; 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 withdrawn, and concealed, under an advancement, in the 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. 



