29 



oped, liiai'titulate, rarely unite radimeutary ; 2iid jiair willi tlie lamelltp 

 more or less elongated. Maxillipeds large, with the masticatory lobes 

 generally largely' develoi)ed and laminar, Imsal lobes miieli smaller and elose 

 together, palji elongated. 4-articnlate. Anterior gnathopoda more or less 

 prehensile, generally not very strong, but sometimes largely developed and 

 .subelielate ; po.sterior ones always very feeble and . slender, highly flexible and 

 furnished with dense tnfts of tactile hairs, daetylns as a rule qnite rudimentary. 

 The 3 posterior ]iairs of pereiopoda successively increasing in length and 

 having the basal joint laminar. Branchial lamellae large, sometimes foblcd 

 transversally on the one or both sides. Incubatory lamellae edged by sleniler 

 setae. Pleopoda rather powerful. Uropoda with the rami more or less lanceo- 

 late, last pair well developed, biramous, generally unlike the preceding pairs 

 and having the outer ramus biartieulate. Telson flattened, entire or more or 

 less deeply cleft. 



Romarls. — The LysianassidiP form a very natural subdivision of 

 the more typical Amphipoda, and in my opinion ought to be classed as a 

 family enually distinct as the ()rchestiida\ Boeck, however, did not regard 

 tliis group as merely a sub-family of the family GammarifJw. Tn the general 

 habitus the numerous forms comprised in this familj' exhibit a rather uni- 

 form appearance, and it is not very long since they were all referi-ed 

 to a single genus,- Ly.vanasf^a . It is the merit of the late Dr. A. Boeck, by 

 a closer examination of the oral parts in the ditferent forms, to have 

 pointed out certain distinctive characters apparently' of generic value. By reason 

 of these characters he found himself alfle to .subdivide the earlier genus Lysimmssa 

 or Aiwmjx into a great number of separate new genera, and, although some of 

 the latter have not lieen sufficiently well characterised, the greater ])ai-t of 

 thorn must, in my o])inion, evidently be supported. The family would seem 

 to be chieflv characteristic to northern latitudes, and in the arctic seas some 

 of the species occur in ijuitc an astonishing abundance, having a great im- 

 portance in (deansing the bottom by devouring the carcasses of the several 

 great mammals, such as whales and seals, which are found there. 



Gen. 1. TrischizOStoma, Boeck, 18G0. 

 Bodj' moderately compressed, with the hark In-oadly rounded. Cepha- 

 lon produced anteriorly over the base of the superior antennre, lateral angles 

 not projecting. Secimd pair of coxal plates much larger than the other and 

 greatly dilated infei'iorly. Epimeral plates of metasome large, roundetl. i^.yes 

 ver^- large, occupj-ing the greater part of the sides of the cephalon. Superior 



Crustacea. 



