1202 THE VOYAGE OF H.M.S. CHALLENGER. 



For this group Gerstaecker gives the following definition : — " Body broad, depressed, 

 head transverse, widened forwards, the eyes projecting laterally beyond the outline of 

 the head, the upper antennae without accessory flagellum. The two front pairs of limbs 

 [first and second gnathopods] not differing in character (nicht formell abweichend) from 

 those which follow [the peraeopods], with the penultimate joint narrow and the terminal 

 small, unguiform." Upon this it must be remarked that both in Icilius australis, 

 Haswell, and in the new species, Icilius danee, there is a small accessory flagellum to the 

 upper antennae ; in Pereionotus, Bate and Westwood say that " the hands of the first two 

 pairs [of legs] are subchelate," and so they are in the new genus Chosroes, while in at 

 least one species of Icilius the third joint in the gnathopods is as usual distinguished from 

 the third joint in the peraeopods by its different position in relation to the fourth joint. 

 The strongly developed third uropods in Chosroes distinguish it strikingly from the other 

 genera. In Icilius and Chosroes the upper antennae are much shorter than the lower, 

 while in Icridium, Pereionotus, and Phlias the upper are the longer. In Icilius and 

 Chosroes the mandibles have a well-developed three-jointed palp, while in Icridium, 

 Grube states that the mandibular palp must be either closely concealed or absent. For 

 Icridium also, Grube, whether rightly or wrongly, denies the existence of a telson. On 

 the mouth-organs of Phlias and Pereionotus nothing, I think, has yet been published. 

 Under these circumstances I provisionally accept the family Icilidse for the two genera 

 which have come under my own notice, both of which have the body broad and depressed ; 

 the eyes lateral, prominent ; the mandibles with dentate cutting edge and secondary 

 plate, strong molar tubercle, and three-jointed palp ; the upper antennas much shorter 

 than the lower ; the telson not cleft. 



Genus Icilius, Dana, 1849. 



1849. Icilius, Dana, Amer. Journ. Sci. and Arts, ser. 2, vol. viii. No. 22. 



1852. ,, Dana, Proc. Amer. Acad, of Arts and SoL, vol. ii. 



1852. „ Dana, Amer. Journ. Sci. and Arts, ser. 2, vol. xiv. No. 41. 



1852. „ Dana, U.S. Explor. Exped., vol. xiii. pt. ii. pp. 833, 844, 1441. 



18G2. „ Spence Bate, Brit. Mus. Catal. Crust. Amph., p. 284. 



1880. „ Haswell, Proc. Linn. Soc. N.S.W., vol. iv. pp. 274, 343. 



1882. „ Haswell, Catal. Australian Crust., p. 275. 



1886. „ Gerstaecker, Bronn's Klassen und Ordnungen, Bd. v. Abth. ii. p. 497. 



For the original definitions of the genus, see Notes on Dana, 1849 (p. 229) and 1852 

 (p. 257). At page 844 of his great work Dana gives a third definition of the genus as 

 follows : — 



" Body much compressed. Antennas elongate, and having long flagella ; the inferior 

 pair longest. Feet not prehensile, all vergiform and unguiculate. Caudal styles six, 

 furcate." In the specific description he explains that "the branches of the last pair [of 



