THOUSANDS OF FATHOMS 219 



a podobranchia to the second maxillipeds, and there are 

 no traces of pleurobranchiae although pleurobranchias are 

 developed on six pairs of appendages. These are riddles 

 which those who have specimens to compare with the de- 

 scriptions may be able to solve. 



Aristeus, Duvernoy, 1841, is distinguished from Penceus 

 chiefly by the circumstance that on the second and third 

 maxillipeds and the first three trunk-legs it has the podo- 

 branchias which the other is without. Aristeus antennatus 

 (Risso) occurs in the Mediterranean and Atlantic, and is 

 described as having a smooth pleon. 



Hepomadus, Spence Bate, 1881, is distinguished from 

 Aristeus by a hepatic tooth on the shoulder of the carapace. 

 Hepomadus glacialis, of which Spence Bate's figures are 

 given in the adjoining Plate on a reduced scale, was taken 

 near Yokohama at the frigid depth of 1,875 fathoms. 



Several new genera from Atlantic exploring expedi- 

 tions have been described in recent years by Professor S. I. 

 Smith, as Hymenop'enceus, 1882, meaning the membrana- 

 ceous Penaeus, Amalopenceus, 1882, which, at least in the 

 type species Amalopenceus elegans, has only the sixth seg- 

 ment of the pleon carinate. Some of the lately described 

 . genera have names alluding to the great depths from which 

 they were obtained : Benthesicymus, Spence Bate, 1881, 

 Benthoecetes, S. I. Smith, 1884, Benthonectes, S. I. Smith, 

 1885, all meaning those that dwell or swim in the aby>- >s 

 of the billowy ocean. Benthesicymus has a submembran- 

 ous integument, exopods to the limbs as in Penceus, podo- 

 branchiaa as in Aristeus, and the last two pairs of trunk- 

 legs longer than the preceding pairs. One of the species, 

 Benthesicymus pleocanthus, Spence Bate, was trawled from 

 a depth of 3,050 fathoms in the North Pacific, while other 

 specimens were taken twenty degrees further south in the 

 smaller depths of 450 and 1,050 fathoms. Bentlionectf* is 

 specially characterised by the multiarticulate flagelliform 

 dactyli, that is the subdivided terminal joints, of the last 

 two pairs of trunk-legs. Xipliopeneus, S. I. Smith, 1885, 

 and Benthoecetes have a corresponding peculiarity in the 

 propodi or sixth joint of the same limbs. In some of the 



