^K 



v'J 



110 



STALK-EYED CRUSTACEA. 



free throughout its length, whereas in Polycheles this process is short and 

 curved, with the distal end flattened in such a fashion as to form a facet 

 which slides over the lower face of the basal segment of the antennules. 



The huge spherical carapace of Eryonicus perhaps serves as a hydrostatic 

 apparatus, by means of which the animal is enabled to lead a free-swimming 

 life at some distance above the ocean bottom. The great depths of the sound- 

 ings at some of the stations where Eryonicus has come up in the trawl may 

 be delusive, as in the case of swimming Hoplophoridcc and SergesUdce^ which are 

 often found in the trawl that has been lowered to great depths. At Station 

 3888, twenty-five miles from the nearest land, where the depth was 1168 

 fathoms, the Tanner self-closing net* was lowered to 400 fathoms and towed 

 for seventeen minutes. The net was then hauled up to the surface after the 

 lower part had been securely closed by the messenger at 400 fathoms. The 

 lower part of the net was found to contain absolutely no life, while the upper 

 part, which had remained open all the way from 400 fathoms to the surface, 

 contained four specimens of Eryonicus^ 19-29 mm. long, together with other 

 swimming forms.f At Stations 3375 and 3383, although captured in the 

 trawl which had been lowered to the depths of 1201 and 1832 fathoms, 

 Eryonicus was found associated with several swimming forms. At Station 

 3403 a specimen of Eryonicus spimilosus was brought up in the trawl where 

 the bottom was only 384 fathoms. 



From these facts it is possible, if not probable, that Eryonicus leads a free- 

 swimming existence at depths moderate compared with those frequented by 

 truly abyssal species. On the other hand, the structure of its visual organs 

 and its absence from collections made with the surface tow-net preclude the 

 thou(>;ht of its living at or very near the surface. 



-1 





Eryonicus csecus Bate? 



Plate B., Fig. 2; Plate XXIX., Fig, 2-2-^ ; Plate XXX, 



?Erj/oneicus caucus Bate, Ann. Mag. Nat Hist., 5th Scr , X. 457, 1883 ; Ecp. Challenger Macrura, pp. 123- 



126, Fig. 30, Plate XII. E, 1888. 

 Ert/onicus caucus ? Tax., Bull. Miis. Comp. Zool. XXIY. 197, 1893. 



Male.—The rostrum consists of a pair of very small spinules. The median 

 ridge of the carapace is armed with small spines arranged thus : 2 (rostral). 

 1. 2. L 1 — 2. 2. 1. 2. There are four minute spinxdes on each side of the 



* For a description of the Tanner net, sec A. Agassiz, Bull. Mus. Couip. Zool., XXllL 40-48, 1892. 

 t See A. Agassiz, Bull. Mus, Comp. Zool, XXIII. 48, 49, 1892. 



