CRUSTACEA FROM THE * CHALLENGER ' EXPEDITION. 43 



Surely these characters of the Podophthalmus males are quite exceptional among Schi- 

 zopods, and much more like what we find in certain Phyllopods thau what we should 

 expect to find among the higher Crustaceans. 



Systematic Position of the Genus. 



The six pairs of leg-like appendages, the rudimentary condition of the ahdominal feet, 

 and the absence of the branchiae assign to this Schizopod its place among the Mysidse. It 

 differs from them only by the free dorsal shield and the presence of breeding-lamellae on 

 seven appendages, which it has in common with the Lophogastridee. It is also sur- 

 prising to find that a member of this latter family has a Mysid character (the subjoints 

 of the legs in Gnathophausia), which, however, is only a peculiarity of one of its generic 

 groups (genus Mysis and subgenera). It accordingly stands in the same relations to 

 Mysidas as Gnathophausia stands to Lophogastridse — there being in both a character 

 which shows some distant relationship to the other group, and both having a free cara- 

 pace, which is not to be found in the hitherto known Schizopods. 



Among Mysidae there are two generic groups -.—Mysis and the genera connected with 

 it, characterized by joints in the tarsal parts of the legs and the absence of branchial 

 appendages on the pleopoda ; and Siriella, in which the legs are simple and terminated 

 by a claw, as in our case, but in which there are branchial appendages on the pleopoda, 

 which Petalophthalmus has not got. This genus therefore belongs to none of these 

 generic groups, and can only be united with the Mysidse if the family characters are so 

 far enlarged as to allow the entrance within it of an animal which has a free dorsal 

 shield and breeding-lamellae on seven appendages. 



The eyes having disappeared, and the eye-stalks having assumed a spherical termi- 

 nation, are of course entirely secondary characters, and probably not even of generic 

 value. 



Characters of the Genus. 



Petalophthalmus*, nov. gen. 



Carapace in no connexion with the five posterior segments of the pereion ; rostrum 

 very short ; three joints in the funiculus of the first antennse ; scale of the second 

 antenna without spines ; labrum subcordiform ; mandibulae having a large manducatory 

 process and a three-jointed palpus. Very strong teeth and setae on both processes of the 

 first maxilla ; second maxilla consisting of a manducatory portion (two elongated pro- 

 cesses and a larger lamellar one), a ciliated flagellum, and a palpus. Maxilliped in 

 both sexes with a lamellar appendage on one of the basal joints ; first gnathopod having 

 the same only in the male; in the female it is elongated, and its last two joints are 

 clumsy and recurved ; second gnathopod and the five pereiopoda leg-like ; pleopoda in 

 the female quite rudimentary, with only one ramus ; in the male somewhat more per- 

 fect, with two rami; telson showing a slight excision at the top; outer appendages 

 jointed. 



No -branchiae on the pereion, nor any branchial appendages on the pleopoda of the 

 male. Seven pairs of hreeding-lamellce at the base of the pectoral appendages. 



* XikraXov and otyQakjAos. 



G 2 



