CARCINOLOGICAL STUDIES. 119 



vioribus", these characters are not present in the male, 

 but the smaller hand of the female agrees better with the 

 original description. 



As regards their length , the five joints of the carpus 

 of the second pair of legs are in proportion to one another 

 as 3:2:1:1:2; the first joint the longest , the second 

 as long as the terminal, the third and the fourth the 

 shortest. The hand has about the same length as the fifth 

 joint of the carpus and the fingers are slightly longer than 

 the palm. 



The three posterior pairs of legs are short and gra- 

 dually decrease in length and thickness. The m e r o p o- 

 dites of the legs of the third pair are armed 

 with an acute tooth at the distal end of their 

 inferior margin; those of the fourth pair are also 

 toothed , but this tooth is exceedingly small and easily 

 overlooked. The terminal postabdominal segment is flat- 

 tened above and armed with two pairs of small spinules 

 in the middle, quite near the lateral margins. 



The male is 17 mm. in length, the female 19 mm. from 

 the anterior margin of the cephalothorax to the end of 

 the telson. According to Stimpson, Alpheus pachychirus 

 attains however a length of 25 mm. 



The indo-pacific species, to which A. pachychirus ^iun^- 

 son is most closely allied, are A. crinitus Dana, A. fron- 

 talis H. M. Edw. and A. latifrons A. Milne Edw. 



A. crinitus Dana differs by its rostrum of ordinary 

 length , by the two terminal joints of the external maxil- 

 lipedes being more elongate, by the structure of the carpus 

 of the second pair of legs , the second joint of which is 

 the longest etc. 



A. frontalis H. Milne Edw., which occurs in the seas of 

 Australia , is also closely allied , but the anterior margin 

 of the cephalothorax projects more forward, the eyes are 

 more prominent and the external maxillipedes are shorter 

 and less slender. 



A. latifrons A. Milne Edw. finally (fig. 15), of which 



Notes from the Leyden JMuseum, Vol. XII 



