Spcci'es of the Isopod Genus Serolis. 301 



Desciij)tions of species of Serolis, even tliose of some recent 

 .lutlior?, tend to be obscure or even niisleadiiijj," as reo-nrds the 

 o'cneral se<;nienti\ti()n of the bod v. Grube'^, desciil)iiig' in 

 certain species a dark transverse line (really a ridge) on the 

 lateral expansions of the segment following the head, regarded 

 it as indicating that this segment was composed of two 

 somites, those of the maxillipeds and first legs (or gnathopods) 

 respectively. On this view the groove or snture-line which 

 marks off the head runs between the maxillary somite and 

 that of the maxillipeds. This interpretation was accejited 

 and clearly enunciated by Beddard (/. c. p. 8), and is more 

 obscurely implied by many subsequent writers. Gerstaecker f 

 confused matters still further by assigning the maxillipeds to 

 the head while stating that the two foUoiclng somites were 

 fused together — an opinion that had the advantage of ac- 

 cf)unting for tlie full number of thoracic terga, but could 

 hardly have survived the examination of a single specimen. 

 As a matter of fact, in Serolis, as in all other Malacostraca 

 with the exception o'i BathynellaX, the first thoracic somite 

 (that of the maxillipeds) is completely incorporated in the 

 head. The articulation between the head and the second 

 thoracic somite, which in most Isopods is more or less 

 movable, is represented in Serolis by a suture-line which 

 corresponds, at the sides of the head, to a deep fold of the 

 exoskeleton, but in the occipital region becomes reduced to a 

 shallow groove. Grube's " dunkle Querlinie," whatever its 

 significance, cannot possibly indicate the limit between two 

 somites. 



The chief differences between the two species composing 

 tlie lalifrons group may be briefly set forth as follows: — 



Dorsal surface of bead and body-somites nearly 



sniootl). Telrioaic segment smooth except for 



u median and a pair of curved submarginal 



ridf^es S. latifroiis, Miers. 



Dorsal surface of head and body-somites stronp-ly 



sculptured. TeLsouic segment studded wit!i 



tubercles between tlia median and subniargiual 



ridges and with a pair of short submedian 



ridges S. heddanli, sp. n. 



Serolis htddardi^ sp. n. (Text-figs. 1-3.) 



Luaditij. — " From stomachs of fish {Trematoinus or Noto- 

 theniii). Deception Island, Branslicld Straits, 5-7 lath. 

 22. 1. 18," 1 $ (holotype), 1 <?. 



• Arch. Natur-. xli. (1) 1875, p. 211. 



t IJronu's 'Thierreich,' Crustacea, i). 19 (18S0). 



X Calmau, Quart. Journ. Micr. fcJci. Ixii. 1917, p. 502. 



