REPORT ON THE CRUSTACEA MACRURA. 629 



following pairs are similar to each other and not very long. The carpos is shorter 

 than the propodos and the dactylos is small, slender, and armed ; the posterior margin 

 of these three pairs is generally fringed with sharp spine-like teeth. 



The pleopoda have the basal joint long, broad, and obliquely compressed, the 

 posterior distal angle being considerably produced, beyond which there are two long, 

 narrow, subfoliaceous plates fringed with hairs, of which the inner is furnished with a 

 compressed stylamblys but without cincinnuli. The first pair differs from the others in 

 having the inner branch short and furnished with a very short stylamblys. The pos- 

 terior pair helps to form the rhipidura, and it has the peduncle short and the branches 

 long and foliaceous. The outer plate is strengthened on the outer side, and longitudinally 

 fluted and furnished with a distinct diasresis, the outer angle of which is armed with a 

 single tooth and spine. 



Each pair- of pereiopoda except the posterior is furnished with a rudimentary mastigo- 

 branchia, and all the branchial plumes increase proportionately very much in size as they 

 proceed backwards. The branchial arrangement is show r n in the following table : — 



Pleurobranchias, 

 Arthrobranchia;, . 

 Podobranchise, 

 Mastigobranchia?, . 



Observations. — This genus has been recently established by A. Milne-Edwards for 

 two specimens taken in the West Indies. Those in the Challenger collection are from 

 the seas around the Philippine Archipelago, and two of them appear to correspond very 

 closely with the occidental species. 



In structural details they correspond very closely with the genus Pandalus, but 

 differ considerably in external form, on which Milne-Edwards has apparently relied for 

 the generic characters. " The carapace," he says, " is carinated above, and the pleon carries 

 upon some of its somites a strong median carina that terminates posteriorly in a point, 

 but the legs are destitute of palps " (basecphyses). Features of this kind are very liable 

 to vary, as may be seen by our species Heterocarpus gibbosus, in which there is neither 

 carina nor tooth on the dorsal surface of the pleon, and yet this species undoubtedly 

 belongs to the same genus as Heterocarpus ensifer, A. Milne-Edwards. 



Geographical Distribution. — The first specimen {Heterocarpus ensifer) of this genus 

 was taken by the Challenger in 1874, near the Philippine Islands, and one very like, 

 if not identical with it, was taken in the West Indies, near Barbados, by the American 

 Expedition in 1878. About the latter time Heterocarpus oryx, A. Milne-Edwards, 

 was taken in the Gulf of Orleans, and another almost identical, Heterocarpus alphonsi, 

 was found by the Challenger near the Philippine Islands ; a slender variety of the same 



