15-i STALK-EYED CRUSTACEA. 



below. The carina on the third abdominal segment is not broken into two 

 parts (except in one specimen), and is armed with only a single spine, at the 

 posterior end. This carina is fluted above, as in H. hosiiUs, from its anterior 

 end to a point corresponding with the position of the anterior spine in the 

 adult II. hostilis. I am inclined to consider these specimens as young stages 

 of H. hostilis, especially since in one of those from Station 3363 the carina of 

 the third abdominal segment, although not two-spined, is nevertheless cut by 

 a notch into an anterior and a posterior section. 



Heterocarpus afflnis Fax. 

 Plate XL., Fig. 2, 2% 2" ; Plate XLL, Fig. 3, 3". 

 Bull. Mus. Comp. Zobl., XXIV. 20-1, 1893. 



This species is closely allied to the preceding {H. hostilis), from which 

 (comparing specimens of the same sex) it differs in the following particu- 

 lars : the rostrum is much shorter in proportion to the length of the cara- 

 pace ; measured from the tip to the posterior limit of the orbit it about 

 equals the rest of the carapace in length in some specimens, while in others 

 it is only two thirds as long. There are, moreover, fewer teeth on its 

 dorsal margin (five or six), the number of teeth on its ventral margin vary- 

 ing from six to ten. The median dorsal line of the carapace is more con- 

 vex, and is arnred, posteriorly to the base of the rostrum, with two acute 

 teeth, whereas in 11. hostilis there is but one tooth on this portion of the 

 carapace, except in a few abnormal individuals. 



It is also nearl}'' related to //. dorsalis Bate, collected off Banda Island by 

 the " Challenger," but differs from that species in having a shorter rostrum, 

 and two median teeth on the third abdominal segment. 



The exopods of the third maxillipcds are the same size as in H. hostilis, 

 whereas in H. dorsalis, according to Bate, they are reduced to a mere 

 tubercle. 



H. affiim and II. hostilis belong to different geographical areas, as will be 

 seen by inspection of the stations at which the two species were procured. 

 H. ajfmis is the more northerly form, from the coast of Mexico (off Acapulco 

 and Cape Corrientes), while //. hostilis comes from the region about the Gulf 

 of Panama. 



Dimensions of a female specimen : length, 153 mm. ; length of carapace, 

 including rostrum, 70 nnn. ; length of rostrum, 35 nun. ; length of antcnnal 

 scale, 23 mm. ; length of telson, 23.5 mm. 



