1920.] 



S. Kemp : Notes on Crustacea Decapoda. 



141 



Text- FIG. 2. — Discias exiil, sp. nov. 

 Chela of ist peraeopod in dorsal view, 



a. Distal end of palm on lower side of 



chela. 



b. Axis on which dactyliis rotates. 



c. Protractor muscle, 



d. Retractor muscle. 



the end of the merus. The basis and ischium appear to be fused. 

 The merus is widest at its distal end and is about twice as long as 

 its greatest breadth ; on the 

 inner side the distal margin 

 is deeply hollowed to receive 

 the hinder end of the chela, 

 which projects backwards 

 beyond the carpus. The 

 carpus is exceedingly small 

 and inconspicuous, consist- 

 ing merely of a thin plate, 

 oval when seen from below, 

 lying between the merus 

 and the chela. The chela 

 itself is thick and heavy, 

 less than three times as long 

 as broad and fully one and 

 a half times as long as the 

 merus. As noted above, the 

 posterior end of the chela, 

 when the limb is straight- 

 ened, fits into a cavity in 

 the distal end of the merus. 

 The structure of the fingers 

 is difficult to make out satis- 

 factorily. When seen from 



below the chela presents the appearance shown in text- fig. 3^. 

 Text-fig. 2 is a dorsal view of a chela which has been cleared 

 in Eau de Javelle. The dactylus is a thin plate or disc, more 

 or less circular in outline which, when it is closed, is ensheathed 

 by more than half its total extent within the propodus. The 

 dactylus is not flat, but saucer-shaped, and the cutting edge is 

 semicircular, at the actual margin thin and transparent and with 

 a band of closely-set striae parallel with the edge. 



The second peraeopod (text-fig. 3c) reaches to the middle 

 of the propodus of the first pair, with exopod extending beyond 

 the end of the merus. The basis and ischium are fused, the 

 merus is little more than three times as long as broad and the 

 carpus is very short and more or less quadrate in outline. The 

 chela is about three quarters the length of the merus and the 

 dactylus about half the length of the palm. On the outer side 

 of the fixed finger there are two long spines. There are two or 

 three small spinules on the cutting edge of the dactylus and one in 

 a similar position on the fixed finger. At the tip each finger 

 bears three or four long, curved, interlocking spines (text-fig. ^d). 



The last three pairs of peraeopods decrease successively in 

 length ; the third (text-fig. y) reach about to the end of the antennal 

 scale, the fifth (text-fig. 3/) scarcely to the distal end of the merus 

 of the first pair. The exopod in the third pair reaches a little 

 beyond the middle of the merus, in the fifth pair to the end of 



