LARVAE OF DECAPOD CRUSTACEA 299 



The young post-larval species here described resembles very closely E. longirostris De 

 Man, having ventral teeth on the rostrum and much the same form of abdominal pleura. 



Although there are several references to and descriptions of these species, the gill 

 formula appears to be still unknown. 



The genus has been regarded by Bouvier, De Man, Ortmann and others as a member 

 of the Nephropsidae, but Miers noted that it was probably nearly related to Eutricho- 

 cheles Wood-Mason. The latter, which was also included in the Nephropsidae, has 

 been shown by Chopra (1933) to belong to the Axiidae, a position also given to it by 

 Balss (1933, p. 87). Chopra indeed finds E. modestus to be so near to Calocaris that it 

 might almost be included in that genus. That being so, it would seem natural to assign 

 the same position to Enoplometopus. 



There is, indeed, little difference between Nephropsidae and Axiidae, but the fact 

 that Enoplometopus has chelae upon leg i only may be taken as sufficient to exclude it 

 from the former. An important character which distinguishes Nephropsidae from 

 Axiidae is the absence in the former of the appendix interna from the pleopods, and to 

 this point De Man alone refers. He states that E. occidentalis has no appendix interna ; 

 but it is well developed in my own post-larval specimens. 



The gill formula of these specimens is unusually complete, since there are not only 

 podobranchs on legs 1-4, but also pleurobranchs. The pleurobranchs are generally 

 reduced, or even absent, in Thalassinidea ; but Iconaxiopsis may have a formula almost 

 as complete as that of Nephropsidae, and in neither family is a pleurobranch found on 

 leg I. In respect to the gills, therefore, this species is more primitive than either, 

 and no systematic conclusion can be drawn from the fact. 



Associated with these specimens at St. 690 were late larvae described below which 

 I regard as belonging to the Axiidae. These larvae agree with Enoplometopus in the form 

 and length of the rostrum, the possession of a well-developed exopod on leg 5, and 

 particularly in the form of the telson, and one is tempted to regard them as belonging 

 to the same species ; but the fact that leg 2 has a well-developed chela seems to make 

 such an identification impossible. It is contrary to all experience that a structure such 

 as this should appear in the larva and be lost in the adult. At the same time it is very 

 remarkable that so many post-larval specimens should be found in the same collection 

 as numerous advanced larvae so closely resembling them and yet of a different species. 



THALASSINIDEA 

 AXIIDAE AND CALLIANASSIDAE 



The only species of Axiidae of which the larvae are certainly known are Axiiis 

 stirhynchiis and Calocaris macandreae, the former described by Webb (1921, p. 406) 

 and the latter by Sars, Bjorck and Bull (1933). In Axiiis stirhynchiis there are only two 

 larval stages, the third stage being post-larval ; but it is not altogether clear how many 

 there are in Calocaris. I have seen two myself, but Bull has described an earlier and 

 Bjorck a later stage, so that there may be four, although the larva is further advanced 



