I. '08. 



100 



The genus Bythocaris may also be recognized at a glance by 

 the great expanse of the antennal scales and by the extra- 

 ordinary development of the supra-orbital spines, which, com- 

 bined with the very short simple rostrum, give the frontal area 

 of the carapace a highly characteristic tridentate appearance. 



Genus Hippolyte, Leach. 



Virbius, Stimpson. 



Two species of this genus are known from British and Irish 

 waters. The branchial formula in each is : — 



Podobranchiae, 



Arthrobranchiae, 



Pleurobranchiae, 



II, 



VIL 



vin. 



IX. 



X. 



XI. 



xn. 



xm. 



XIV. 



ep. 



ep. 











... 



1 









1 



1 



1 



1 



1 



Rostrum scarcely as long as carapace, with a pro- 

 minent dorsal tooth at base ; carapace (vvith 

 rostrum) three times as long as deep ; cornea 

 large ; antennal scale less than three and a half 

 times as long as broad ; third pereiopods 

 reaching almost to apex of antennal scale, 



H. varians. 



Eostrum longer than carapace, usually without a 

 dorsal tooth at base ; carapace (with rostrum) 

 four tunes as long as deep ; cornea much 

 smaller ; antennal scale fully four and a half 

 times as long as broad ; third pereiopods reach- 

 ing only to ultimate segment of antennal 

 peduncle, . . . H. prideauxiana (p. 101). 



Hippolyte varians, Leach. 



PI. XIII, figs. 1-7. 



Hippolyte varians, Bell, 1853, fig., p. 286. 

 Hippolyte fascigera, Gosse, 1853. 

 Hippolyte varians, Walker, 1899. 



The striking colour variations^ which this abundant species 

 presents have been repeatedly noticed ; no detailed description 

 of the numerous phases is necessary hero. 



1 This species has formed the subject of a very important memoir 

 by Keeble and Gamble (1900, 1904, and 1905) on th^ colour physiology 

 of the higher Crustacea, 



