1SG8.] MR. C. SPENCE BATE ON NEW FRESHWATER PRAWNS. 363 



4. On a new Genus, with four new Species, of Freshwater 

 Prawns. By C. Spence Bate, F.R.S. 



■ (Plates XXX. & XXXI.) 



Macrobrachium, gen. nov. 



Carapace armed anteriorly with a vertically projecting rostrum. 



Eyes with short peduncles, not concealed beneath the carapace. 



Superior antennae having the first joint of the peduncle caved 

 upon the upper surface ; second and third joints cyhndrical. Fla- 

 gella three-branched, the smallest branch united to the largest. 



Inferior antennae furnished with a large scale ; flagellum long 

 and slender. 



Mandibles having a molar and an incisive process, and furnished 

 with a triarticular appendage. 



Gnathopoda pediform. 



First pair of pereiopoda slender, about as long as the carapace, 

 didactyle ; second pair immensely developed (in the male), longer 

 than the entire length of the animal from the extremity of the ros- 

 trum to that of the telson. 



Posterior three pairs simple, robust. Posterior pair of pleopoda 

 longer than the telson. Telson triangular, terminating in a single 

 point. 



Macrobrachium americanum, sp. nov. (Plate XXX.) 



Carapace nearly half the length of the animal. 



Rostrum short, armed above with eleven anteriorly projecting 

 dental processes, of which the last four are posterior to the orbital 

 margin of the carapace, and furnished with short, stiff hairs in the 

 depressions between the teeth ; below with three simple teeth. The 

 rostrum has the anterior portion depressed, the apex being slightly 

 elevated. Behind the margin, at the lower extremity of the orbit, 

 is a single, sharply pointed tooth, behind and below which is a 

 sharp spine or tooth that is surrounded at the base by a suture that 

 passes from it on the anterior side to the anterior margin of the 

 carapace. 



Pleon deep, scarcely longer than the carapace. 



Eyes globular. Superior antennae having the peduncle scarcely 

 longer than the rostrum ; first joint half the length of the peduncle, 

 inner surface flat, perpendicular, furnished with a single tooth near 

 the centre of the lower edge, superior surface concave (for the lodg- 

 ment of the eye) ; outer margin thinned out to a fine edge, fur- 

 nished with a sharp, anteriorly directed tooth near the centre, and 

 another at the distal extremity ; the next two joints are short. 

 The smallest flagellum united to the largest for about one-fourth of 

 an inch from the base. Inferior antennae having the peduncle 

 about half the length of the superior. The large squamiform pro- 

 cess nearly half as long again as the rostrum, furnished with an ex- 

 ternal subapical tooth. Flagellum about as long as the second pair 



