BORRADAILE— ON THE PONTONIIN^ 325 



it the results of the examination of a small but interesting collection made by him 

 in the Torres Straits, which contained three species new to science, one of them the 

 representative of a new genus. I have also re-examined the material in the Cam- 

 bridge University Museum of Zoology, and am under much obligation to Dr W. T. 

 Caiman for enabling me to do the same with the Pontoniinse of the British Museum. 



I have not restricted myself to the systematics of the subfamily. The un- 

 fortunate destruction in transit of a great part of the crustaceans collected by myself 

 in the Island of Minikoi has deprived me of the numbered specimens to which my 

 field notes applied, and thereby rendered it impossible for me to give information upon 

 the natural history of various prawns, but I have endeavoured to elucidate to some 

 extent the conditions under which Pontoniinse live, and the connection between their 

 structure and their habits. It has seemed to me advisable also to discuss briefly 

 certain questions of morphology and genetics, and impossible to omit consideration of 

 the relationship of the genera of Pontoniinse wath one another and with other prawns. 



Short definitions of the new species and of three of the new genera have 

 already appeared in the Annals and Magazine of Natural History for February, 1915. 

 Fuller diagnoses, with notes on some other species, will be found in the course of the 

 present article. 



A Monograph of the Pontoniinse. 



It is one of the paradoxes of Marine Natural History that the Decapod Crustacea, 

 the most active and nervous of the invertebrates of the sea, are also among the most 

 prone to avail themselves of opportunities of shelter and concealment, and make use 

 of the most subtle adaptations to this habit. In describing the collection of crabs 

 made by Professor Gardiner and myself in the Maldive Islands and Minikoi*, I found 

 occasion for some remarks upon this phenomenon with regard to the various groups 

 of Brachyura. Among the prawns, two families are pre-eminent in the same respect. 

 Professor Coutiere's fine researches upon the Alpheidse have illuminated one of these 

 cases. The other is that of the Pontoniinse. Although the members of this group 

 have not so rich an originality as have the Alpheidse in the production of bizarre 

 modifications of structure, they are in one way even more interesting, for they show a 

 more complete series of stages in the transformation of the primitive caridoid facies, 

 ranging from wholly free-living forms such as Urocaris to commensal and very con- 

 siderably degenerate genera such as Conchodytes. The success which has attended 

 their strategy of retreat makes them so abundant that they bulk largely in any well- 

 made collection of prawns from the Tropics, and their species are numerous and often 

 closely related, though generally perfectly distinct. Moreover, the assembling of the 

 species into genera and other groups is a matter of great difiiculty, partly because 

 they present an almost unbroken series of degrees of modification, associated, no doubt, 

 with a gradually increasing dependence upon the host, and partly because among 

 species of similar habits similar features reappear with bewildering frequency. They 

 are therefore of as much importance to the systematist as to the naturalist. 



* Gardiner's Fauna of the Maldives. 



