1868.] MR. C. SPKNCE BATE ON NEW FRESHWATER PRAWNS. 367 



with the outer niargin of tlie second articulate margin ciHated, ex- 

 tremit)- of both plates round. Telsoii smooth, laterally slightly 

 compressed ; near the base on the central dorsal surface is a depres- 

 sion occupied by a small tuft of hair, and beyond the middle, on 

 each side, are two short spines and a fasciculus of short hair. 

 Hah. Tambo River. 



The near resemblance that these species bear to those of the 

 genus PalcBmon may induce some carcinologists to reconsider the 

 propriety of making these species a genus by themselves. I am not 

 aware that any structural distinction separates them from the genus 

 Palcemon. There is, I think, however, in the enormous length of 

 the second pair of pereiopoda, when compared with the same ap- 

 pendage in Palcemon, a strong prima facie evidence that a separate 

 generic distinction would form a very natural classification. I had, 

 I must admit, some doubts upon the question, and hesitated in my 

 opinion until I found that others, though closely allied in general 

 form, yet specifically distinct in character, enabled me to see that 

 the pecuHarly distinguishing features that separated the species of 

 this genus from Palcemon were sufficiently constant to warrant 

 the adoption of the new genus. The convenience of this arrange- 

 ment may also be seen in the peculiar and distinct habitat of 

 Macrobrachium, the whole of the species yet known being lacustrine 

 or fluviatile. I have only seen one or two specimens of each spe- 

 cies, and these are all males. The development of the chelopods 

 is so great in length that it must be difficult, if not impossible, 

 for the animal to reach its own mouth with them ; so that thev 

 can be of no use in feeding, for which purpose the first pair, being 

 shorter, are more efficient. I believe it probable, but have not been 

 informed, that in the females the chelopods are less monstrously 

 developed. 



It is something very remarkable that these Prawns, all of them 

 so very large, living in freshwater lakes and rivers, in localities so 

 very distant from each other as Central xlmerica and Central India, 

 should bear so near a resemblance. 



We arc not aware that the same rivers or lakes have any other 

 species of Prawn ; and it would appear that the several species must 

 have come from one common origin ; for even the position and 

 number of the spines on the telson, as well as the fasciculus of hair 

 in the small depression at the base of the same, are common to all 

 the species. 



Whether or not there is anything remarkable in the form of their 

 young or in the development of their larvae I know not. The fresh- 

 water Astaci differ from their marine congeners in producing the 

 young in a more advanced stage of development ; but this appears 

 not to be a constant law in freshwater Crustacea. In a small fresh- 

 water Prawn from the rivers of the island of Mauritius, that has 

 been sent to me by Dr. Power, the young undergoes a change of 

 form similar to that of the marine species. 



I look upon the discovery of these edible Crustacea as being 



