SCHIZOPODA. 33 



Mysidetes posthon. 



(PI. VII., Figs. 1-13.) 

 Mysidetes posfhon. Holt and Tattersall, 1906 (1). 



Localities of captures: — Off Coulman Island, 100 fathoms, one specimen, male, 

 25 mm. 



Winter Quarters, 5. 6. 02. 56 fathoms, one specimen, female, 23 mm. 



Winter Quarters, 29. 8. 03. No. 12 Hole, 25-30 fathoms, three specimens, two 

 females and one male, 21 mm. 



General form (Fig. 1 ) compact and moderately robust. 



Carapace (Fig. 1) leaving the last segment of the thorax exposed posteriorly ; 

 antero-lateral margins produced into a short obtuse rostrum not extending beyond 

 the eyestalks ; antero-lateral corners rounded, cervical sulcus well marked. 



Pleon (Fig. 1 ) longer than the carapace ; first five segments sub-equal in length ; 

 sixth segment about once and a half to twice as long as the fifth. 



Eyes (Fig. 1 ), large, globose ; pigment brown. 



Antennular peduncle (Fig. 2) much shorter than the antennal scale ; basal joint 

 longer than the terminal joint, and having its outer corner produced beyond the 

 distal extremity of the second joint, the produced part tipped with four or five long 

 setae ; second joint small ; third joint almost square in shape ; antennular brush in 

 the male rather small and feebly hirsute. 



Antennal peduncle (Fig. 3) slightly shorter and more slender than the antennular, 

 and little more than half as long as the scale ; third joint shorter than the second. 



Antennal scale (Fig. 3), lanceolate in shape ; between four and five times as 

 long as broad ; setose all round ; a minute second joint at the apex ; a spine on the 

 outer distal corner of the basal joint. 



Mandibles (Fig. 4) with a well-developed molar process and cutting edge ; palp 

 (Fig. 5) with the second joint somewhat expanded and armed with long setae on 

 both margins ; third joint not much expanded, a row of strong plumose setae on 

 the lower edge, and two very strong simple spine-like setae at the tip. 



Second maxillae (Fig. 7) with the setiferous expansion of the basal joint well 



developed. 



Endopods of the first thoracic limbs (Fig. 8) of about the same build as in the 

 genus Mysidopsis, but seven-jointed ; masticatory lobe well developed ; inner margins 

 of the proximal four joints armed with numerous plumose setae ; sixth joint bearing 

 a well-developed nail and beset with numerous plumose setae. 



Endopods of the second thoracic limbs (Fig. 9) very similar to those of Mysidopsis ; 

 longer than the first ; sixth joint armed with numerous plumose setae, but in the 

 specimen dissected I was unable to detect a nail, though it may have been 

 broken off. 



