THE GENUS CHORISMUS 



387 



This stage differs very little from stage I, but can be most easily separated by the 

 presence of a spine on the antennal scale. 



Stage III. Length 11 mm. (Fig. 98). 



Rostrum a trifle longer than antennular peduncle ; with five dorsal teeth and either 

 smooth or with one small spine below. Telson with posterior margin straight; width 

 at end more than half length (58 : 99), with 10 + 10 spines. Antennule with stylocerite, 

 and with inner branch as long as outer, both unsegmented. Flagellum of antenna about 

 4 mm. Legs almost fully developed, legs i and 2 with large chelae. Carpus of leg 2 

 divided into four segments. 



Exopod of maxillipede i not widened at base and without setae in this position. 

 Epipods of maxillipede 3 and legs i and 2 absent in one of two specimens examined, but 

 traceable in the other. No trace of arthrobranchs. 



Pleopods large, without setae. Uropods fully developed. 



Of sixty-nine seen only six were in this stage, which is no doubt the last larva. 



Post-Larval Stage L Length about 16 mm. (Figs. 99-105). 



Rostrum slender, not widening towards end, with 6-8 dorsal teeth and 3-4 ventral. 

 Carapace without supra-orbital spine; with antennal and pterygostomial spines. Ab- 

 dominal somites 3 and 4 slightly gibbous ; pleura of somite 5 slightly pointed. Telson 

 parallel-sided, about three times as long as wide, with two pairs of lateral spines and 

 12-16 slender spines on the slightly convex posterior margin. Anal spine large. 



The appendages are all nearly of adult form. Mandible with small rudiment of palp. 

 Carpus of leg 2 of eight segments. 



Exopod of maxillipede 3 large, without setae. Legs 1-3 with large vestigial exopods. 

 Gill formula and epipods as in adult, but no arthrobranch seen on maxillipede 3. 



Some specimens differ in having no trace of an exopod on leg 3 and those of legs i 

 and 2 reduced to small papillae, while somites 3 and 4 are not gibbous; but they are 

 either of the same size, or but little larger, and do not seem to represent a second 

 stage (Fig. 99). 



Measurements of leg 2 (in mm.): 



Coutiere (1905, p. 26; 1907, p. 15) has suggested that the larva described by him as 

 Hippocaricyphiis bigibbosiis may belong to Chorismus. The possibility that it might be 

 C. antarcticus is now excluded, and it is most unlikely that the development of C. tuber- 

 ciilatiis could differ so profoundly as Coutiere 's supposition would require. Coutiere 's 

 larvae were taken at two stations in the central Atlantic,^ a fact which, in itself, would 

 seem to exclude their identification with a genus confined to the Antarctic. 

 1 St. 1851, 36^^ 17' N, 28° 53' W; St. 2187, 38° 04' N, 26° 07' W. 



