SYSTEMATIC ACCOUNT ,69 



In his discussion on the position of this subfamily amongst the Idoteidae, Nordenstam stresses the 

 systematic value of the morphology of the coxal plate ; he points out that the type of plate found in 

 members of the Macrochiridotheinae does not occur in members of the other subfamilies. I cannot 

 agree with this statement, for, in some of the species of Edotia belonging to the subfamily Idotheinae, 

 coxal plates are developed on the coxal joints of the last three pairs of thoracic limbs and these extend 

 on to the dorsal surface where they are separated from their respective terga by sutures. The coxal 

 joints of the second, third and fourth pairs of pereiopods can be seen in lateral view of Edotia, as well 

 as in the species of Macrochiridothea. In Glyptonotus (subfamily Glyptonotinae), a similar arrange- 

 ment occurs, but the bases of the limbs of the first four pereion somites are hidden by the development 

 of the pleura. As has already been pointed out, in members of all the subfamilies coxal plates are 

 developed on the inner sides of the coxal joints; these cover the ventral surfaces of their respective 

 somites, and meet and sometimes fuse in the mid-ventral line. 



A character peculiar to the species of Macrochiridothea is that the coxal joint of the first pereiopod 

 is only partially fused with the tergum of its somite ; a similar condition can be observed, though to 

 a less extent, in Pseiididothea bonnieri Ohlin. 



It is difficult to understand why Nordenstam placed the two genera Chiriscus and Macrochiridothea 

 together in a new subfamily, the only character which they have in common being the 'markedly 

 subchelate (seroliform) ' first pereiopods. The second and third pairs in the species of Macrochiridothea 

 are prehensile, but considerably weaker than the first pair, whereas in Chiriscus australis the second 

 and third pairs are not prehensile, and are very similar to the fourth, fifth and seventh pairs. Ac- 

 cording to Richardson (191 1, p. 169), the sixth pair of legs is much longer than the others and is the 

 only pair in which a dactylus is present. 



The genus Macrochiridothea appears to be more closely allied to Mesidotea than to any other form. 

 The two genera have the following characters in common: 



(i) The head is laterally expanded, and the lateral margins are cleft. 



(2) The eyes when present are dorsal and submarginal. 



(3) The antennule is shorter than the antenna and its flagellum consists of one or two joints. 



(4) The first three pairs of pereiopods are prehensile. In Macrochiridothea the first pair is markedly 

 subchelate (seroliform) and the second and third pairs are considerably weaker, whereas in Mesidotea 

 the three pairs are approximately of equal size. The remaining pairs of limbs are ambulatory. 



(5) The abdomen consists of four free segments (fourth partially fused with the pleotelson in 

 Macrochiridothea) and a pleotelson. 



(6) Uropods with both an exopod and an endopod ; the former in Mesidotea is always more or less 

 rudimentary. 



The two genera diff'er from each other in the number of joints to the maxillary palp; this number is 

 five in Mesidotea and four in Macrochiridothea. They also diflFer in the coxal joints of the pereiopods, 

 which in Mesidotea, with the exception of the first, are expanded into coxal plates which extend on to 

 the dorsal surface and are separated from their respective terga by sutures ; in Macrochiridothea these 

 plates are only developed on the last three pairs of pereiopods; they also are separated from their 

 respective terga by sutures. 



The family Idoteidae is in much need of revision ; its members, taken as a whole, are closely related 

 to each other, consequently it is difficult to select the morphological characters on which a classification 

 should be based. 



Whether or not the two genera Chiriscus and Macrochiridothea should remain together in the 

 subfamily Macrochiridotheinae is doubtful, but it seems wisest to leave them in their present position 

 until a revision of the whole family can be undertaken. 



