I9I5-] 



Fauna of the Chilka Lake ; Crustacea Decapoda. 



239 



margin, forming a very rudimentary tooth behind the outer orbital angle. In 

 5. ander soni a short ridge is to be found on either side of the carapace strictly 

 transverse in direction and situated close behind the middle of the orbit. Of this in 

 5. batavicum there is no trace. 



The chelipedes are almost or quite equal. In the largest specimens the ischium 

 bears a small blunt anterior tubercle and, in all, the antero-inferior edge of the merus 

 is produced distally in the form of a thin triangular crest, apically blunt or rounded 

 and anteriorly serrate. The inner angle of 

 the carpus is rectangular ; behind it on the 

 postero-internal face of the segment there 

 is, in both sexes, in addition to the short 

 black hairs on the upper surface noticed 

 by de Man, a linear series of very long stiff 

 setae, also black in colour, and a row of 

 similar but shorter setae extends diagon- 

 ally across the smooth inner face of the 

 merus. The palm of the chela bears on its 

 upper surface the characteristic ridges 

 figured by de Man. In the male the outer- 

 most and best developed of these ridges 

 extends in a sinuous line from the inner 

 end of the dactylar articulation to a point 

 close to the mid-dorsal projection of the 

 carpus (text-fig. 15e). This ridge is com- 

 posed of horny tubercles, the anterior of 

 which are very high and upstanding. In- 

 wards of this limiting ridge are several 

 others, also tubercular but for the most 

 part shorter. One of these defines the margin of the hand and, in the space between 

 it and the primary ridge, and more or less parallel with portions of the latter are two 

 or three other ridges and a few odd tubercles. Below the marginal ridge on the upper 

 and inner face of the palm are other less conspicuous rows of tubercles. The precise 

 arrangement of the ridges is somewhat variable ; it corresponds comparatively closely 

 with de Man' s figure, though one would gather from his description that only two 

 dorsal ridges existed. The tuft of hairs found on the outer surface of the fingers 

 is conspicuous in all males (text-fig. 15a), but, owing perhaps to the small size of 

 the specimens, does not occupy such a long area in lateral view as is shown in the 

 original figure. The hairs extend through the base of the finger-cleft and are visible 

 on the inner side. The fingers in other respects agree in the closest manner with de 

 Man's description, but possess more teeth, often as many as six, on their cutting 

 edges. 



The chela of the female bears on the upper surface ridges closely comparable to 

 those of the male ; there are, however, only a few sparse hairs at the base of the 



Fig. 15. — Sesarma batavicum, Moreira. 



a. Right chela of male, external view. 



b. Left chela of male, viewed obliquely from above. 



