202 STALK-EYED CRUSTACEA 



The branchial formula is as follows : — 



23 + lr+(6) 



With the exception of those on the tenth and fourteenth somites the 

 pleurobranchiae are very small and might be called rudimentary if it were 

 not for the plumose structure of all but the one on the thirteenth somite. 

 The podobranchiae decrease in size posteriorly until, on the antepenultimate 

 pair of legs, they are reduced to small and weak organs. 



If the branchial formula of Hemipeneiis be compared with that of Aristcms 

 (page 195), it will be seen that they are very nearly alike ; the difference 

 consisting in the further reduction in size of the pleurobranchite in the 

 latter genus, and the complete disappearance of the podobranchia of the 

 twelfth somite, which is very small, be it observed, in Hcmipcneus. In its 

 facies Hemipeneus differs considerably from Aristceus. It has a slenderer body, 

 flattened eye-stalks, longer antennular peduncles and antennal scales, peculi- 

 arly long-fingered chelaa and flattened meri on the chelipeds, and long, 

 exceedingly slender, styliform ultimate and penultimate thoracic appendages. 



The largest specimen of this species, — a female from Station 3400, — 

 measures 245 mm. from the tip of the rostrum to the end of the telson. The 

 rostrum of this specimen is 56 mm. long, the whole carapace, including 

 rostrum, 116.5 mm. 



Hemipeneus triton Fax. 



Plate Z., Fig. 1-T. 



Bull. Mus. Comp. Zool., XXIV. 215, 1S93. 



This species, like H. spinidorsalis, is remarkable for having a long, curved 

 spine on the dorsal side of the third abdominal segment. It differs from 

 H. spinidorsalis in having a very much shorter rostrum and longer, more 

 flattened, ribbon-like outer antennular flagella. The rostrum is shorter than 

 in any previously described species, being much shorter than the eye-stalks ; 

 it is armed above with two to four teeth, the posterior of which lies a little 

 way behind the orbit; the fourth tooth, when present, is very minute, and is 

 situate near the distal end of the rostrum. The rostrum is the same length 



