CRUSTACEA MALACOSTRACA. III. , 2 , 



stinct Mandibles very thick and peculiarly .shaped ; the incisive part short and obtuse, movable lacinia 

 small or wanting, seta short or wanting, molar process either rather slender, tapering tu the obtuse, 

 setiferous end, or very reduced, being a very thin and somewhat or very short process with terminal 

 Mte. Palp of the maxillipeds with second joint long and broad, third joint short and broad, the two 

 distal joints well developed; epipod broad, moderately long. - Thoracic segments movable, divided 

 into two sections, and the three posterior segments very different from the four anterior ones. The two 

 anterior pairs of legs somewhat prehensile, with second joint very long, considerably or much longer 

 tli.iu the third; third and fourth pairs moderately or very long, with second joint short, while the third 

 is extremely long. The three posterior pairs, at least fifth and sixth pairs, natatory; fifth joint com- 

 pressed and expanded especially on fifth pair, sixth joint somewhat or scarcely expanded, and both 

 these joints most frequently, and at least on fifth pair, equipped with natatory seta: along the upper 

 margin or at both margins; seventh joint long. -- Abdomen triangular, with the narrow end obtuse 

 or acute. Uropods ventral, somewhat small; peduncle flattened, oblong-oval, with numerous marginal 

 seta:; endopod much shorter than the peduncle, exopod minute or wanting. 



Remarks. The family Muunopsidae as limited by Sars in his Account can be divided into 

 three very natural groups. All agree in having the antenna: elongate, at least third and fourth pairs 

 <>t legs moderately to extremely long, and at least fifth and sixth pairs, generally also seventh pair, 

 natatory, but they differ from each other in several characters, such as the position of the antennnUc, the 

 shape and structure of the mandibles, the relative length of second and third joints iti third and fourth 

 pairs of legs, the posterior thoracic segments and the uropods. One feature is remarkable, viz. that 

 while in the Ilyarachnini the third and fourth pairs of legs have the second joint short and the third 

 extremely long, more than twice as long as the fourth, we find in the Eurycopini the second joint 

 long, about as long as or much longer than the third, which is longer or shorter than the fourth, and 

 in the Munnopsini both second, third and fourth joints in the same two pairs of legs short 



The group comprises four genera established by Sars, viz. llyarachna, Echinozonf, Aspidarachna 

 and foeudarathna, but only the two first-named genera are represented in the material from the "In- 

 golT arcs. 



llyarachna G. o. Sars. 



The generic characters have been well pointed out by Sars, excepting as to the antennukr. 

 He wrote in the Account (p. 134135): "Superior antenna: originating close together from the front, 

 basal joint large, sub-quadrangular in form, inner corner somewhat more projecting than the outer . . ." 

 Sars figured his /. drnticulata (PL 61) as having the inner distal comer of the basal joint of the anten- 

 nula- slightly produced and the outer corner strongly produced, which is correct, but opposed to his 

 statement quoted. In /. longicornis G. O. S. and /. hirtifffs G. O. S. he figured the outer corner of 

 the same joint as slightly, the inner as strongly, produced, which is in accord with his generic diag- 

 nosis, but is in reality wrong; in all species of llyarachna the antennular basal joint has the portion out- 

 side the articulation of second joint produced into a very conspicuous, more or less triangular plate, 

 while the distal inner comer is slightly or scarcely produced, 



TW UtoMByifcloi. IIL f . I* 



