364 MR. c. sPENcn bate on new freshwater prawns. (May 28, 



of pereiopoda. Mandible having the incisive margin tridentate, the 

 molar tubercle strong, prominent, and quadrate, and the triarticulate 

 appendage not longer than the incisive process. Gnathopoda sub- 

 equal, short, robust. First pair of pereiopoda slender, having the 

 carpus longer then the meros, and nearly four times as long as the 

 propodos, smooth. Second pair of pereiopoda half as long again 

 as the entire animal, having the carpus shorter than the meros, and 

 not half as long as the propodos ; digital process turned inwards, 

 armed within the centre with a large dental tubercle ; dactylus 

 meeting the digital process of the propodos at the extremity only, 

 and armed near the centre with a large dental tubercle. The entire 

 appendage covered with short spinous denticles, that are strongest 

 on the inner surface and thickest on the digital process of the pro- 

 podos, the dactylus, as well as the carpus, meros, and basal joints. 

 Last three pairs of pereiopoda robust, spinous along the surface of 

 the carpus, propodos, and dactylus. Posterior pair of pleopoda 

 having the outer ramus biarticulate, the margins round and smooth. 

 Telson shorter than the posterior pair of pleopoda, furnished with 

 a fasciculus of hairs near the base, and two sublateral dorsal spines 

 beyond the centre. 



This very interesting and, from its great size, valuable Prawn, 

 was obtained by Mr. Osbert Salvin from the Lake of Amatitlan, 

 whence a considerable number are procured and brought to the 

 markets in Guatemala. Its length, from the tip of the rostrum to 

 the extremity of the telson, is about 9 inches ; and in diameter it is 

 about 5 inches. The length of the great claws is a feature that 

 must separate this from the genus Palcemon, from which it is also 

 distinguished by its less slender and graceful proportions. The 

 colour of the specimen, as we have it dead, is of a brimstone-yellow, 

 longitudinally striped with dark blue along the dorsal surface and 

 on the sides of the pleon. 



Macrobrachium formosense, sp. nov. (Plate XXXI. fig. 1.) 



Carapace about one-third the length of the animal, having a 

 rostrum nearly half the length of the carapace, armed above with 

 eleven teeth, two of which are behind the orbital margin of the 

 carapace, and furnished with short, stiff hairs between the teeth. 

 Inferior margin smooth, fringed with short hairs. Behind the 

 margin of the lower angle of the orbit is a sharp anteriorly pointed 

 tooth, and obliquely behind and below is a second similar tooth. 

 First pair of antennae having the peduncle rather shorter than the 

 rostrum, the first joiut of which is about half the length of the 

 peduncle, concave upon the upper surface, and furnished with a 

 sharp distal tooth on the distal outer angle, and a row of hairs along 

 the outer margin. The smallest branch of the flagella is united to 

 the largest for about one- tenth of an inch. Second pair of antennae 

 having the squamiform appendage reaching beyond the rostrum, 

 and armed subapically on the outer side with a short, sharp tooth. 

 I'Mrst pair of pereiopoda slender, long, having the carpus longer 

 than the meros, and three times as long as the propodos. Second 



