Species of the Isopod Genus Serolis. 301 



Descriptions of species of Serolis, even those of some recent 

 authors, tend to be obscure or even misleading- as regards the 

 general segmentation of the body. Grube*, describing in 

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

 lateral expansions of the segment following the head, regarded fc 

 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 suture-line which 

 marks off the head runs between the maxillary somite and 

 that of the maxillipeds. This interpretation was accepted 

 and clearly enunciated by Beddard (I. 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 following somites were 

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

 counting for the 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 of Bathynella\, 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 

 the latifrons group may be briefly set forth as follows : — 



Dorsal surface of head and body-somites neariy 



smooth. Telsouic segment smooth except for 



a median and a pair of curved submarginal 



ridges S. latifrons, Miers. 



Dorsal surface of head and body-somites strongly 



sculptured. Telsouic segment studded with 



tubercles between the median and submarginal 



ridges and with a pair of short submedian 



ridges S. beddardi, sp. n. 



Serolis beddardi, sp. n. (Text-figs. 1-3.) 



Locality. — "From stomachs of fish (Trematomus or Noto- 

 thenia). Deception Island, Bransfield Straits, 5-7 fath. 

 22. 1. 18," 1 $ (holotype), 1 tf ■ 



* Arch. Naturg. xli. (1) 1875, p. 211. 



t Bronn'a 'Thierreich,' Crustacea, p. 19 (1880). 



I Caiman, Quart, Journ. Micr. Sci. Ixii. 1917, p. 502. 



