660 MR. E. J. MIERS ON A COLLECTION OF [Juiie 19, 



teeth of the rostrum are variable in number in diiferent examples of 

 the same species ; and even the comparative length of tlie joints 

 of the second pair of legs (which affords excellent specific characters 

 when taken from adult animals) is less trustworthy in younger speci- 

 mens. 



After having examined a considerable number of species of this 

 genus, I may express my behef that some of them — perhaps some 

 even of those included in the present paper — will, upon comparison of 

 larger series of specimens than we at present possess, be found to repre- 

 sent merely different stages of growth of the same animal. Dr. von 

 Martens, in two papers in the Archiv f. Naturgeschichte, xxxiv. 

 p. 34 (1868), and xxxv. p. 32 (1869), has done good service toward 

 elucidating this difficult genus by exhibiting in a tabulated form the 

 diagnostic characters of the species inhabiting the Eastern-Asiatic 

 Region, and South Brazil. 



Pal^mon nattereri. 



Palcemon nattereri. Heller, Kais. Akad. Wissensch. Sitzungsber. 

 xiv. Abth. i. p. 414, pi. ii. fig. 36, 37 (1862) ; von Martens, Archiv 

 f. Naturg. xxxv. p. 32 (1869). 



Hub. Guiana (river St. Laurent) (JeluM). 



This species was described by Heller from specimens collected by 

 Natterer in the Rio Negro, Brazil. Ii is distinguished from its 

 congeners from the American continent by the elongated, strong, 

 second pair of legs, which are closely spinulose, and of rather unequal 

 size ; the palm is much longer than the wrist ; the upper (mobile) 

 finger has two, the lower a single strong tooth on its inner margin. 

 The sides of the carapace below the hepatic spine are very rough 

 and scabrous to the touch. Two specimens are in the collection, 

 which I refer to this species : in the larger (length to anterior 

 margin of carapace 2 inches) the rostrum is imperfect ; in the smaller 

 the rostrum ^^ is toothed. In the smaller specimens; as is always the 

 case in the species of the genus Palcemon, the distinctive characters 

 are far less strongly marked. 



Pal^mon brasiliensis. 



Palcemon brasiliensis. Heller, Kais. Akad. Wissensch. Sitzungsb. 

 xiv. Abth. i. p, 419, pi. ii. fig. 46 (1862); von Martens, Archiv f. 

 Naturg. xxxv. p. 32(1869). 



Hab. Guiana (R. St. Laurent) (Jelski). 



Three specimens of this species are in the collection ; the length 

 of the largest is 1 inch 10 lines to tip of rostrum. Two specimens 

 agree well with the figure and description of Dr. Heller, whose 

 specimens were collected by Natterer in a brook at Camaroes, in 

 Brazil. It is to be noted, however, that the second pair of legs, 

 whicii he describes as unequal, are, in the specimens from Guiana, 

 very nearly of equal length. 



This species was found in the same stream ivith the precediiig. 

 The legs are not so robust, and more minutely spinulose, the palm 



