NO. 13-0. XATIUIAL IIIsroRY OF THE IS< il>< )I)A— RICHARDSON. 5 



segmented. In the Entoniscida^ alone there is no trace of segmenta- 

 tion whatever in the adult fenialc, and in tlu> C'ryptoniscidEe but slight 

 traces of segmentation. 



Man}' of the terrestrial Isopoda, the pill hugs, and some of the 

 Spha>romidie, especiall}" the genus Spharoma Latreille, are able to 

 roll the ])od3' completel}' into a ball. 



The head may be considered as composed of seven coalesced seg- 

 ments, indicated b}- the number of paired appendages, the last 

 coalesced segment, represented by the maxillipeds, being derived from 

 the thorax. The eyes may be regarded as the appendages of a first 

 or ocular segment; the antennaj and antennuhe, the appendages of a 

 second and third segment; the mandibles and the two pairs of maxillse 

 representing the fourth, fifth, and sixth segments; the maxillipeds, as 

 already' stated, represent a first thoracic segment, which is perma- 

 nently united with the head in all Isopods, the name foot-jaws indi- 

 cating their origin and function. (Harger.) 



A second thoracic segment, which is usuall}" the first free segment, 

 is also consolidated with the head to form a carapace in the Tanaidai 

 and the vSerolida?; in the latter family sutures may or may not be pres- 

 ent. The Australian species Crahyzos longicaudatus Spence Bate, 

 as well as Arcturides cornuUn^ Studer, and Stenasellus Dollf us have the 

 head and first free segment of the thorax united so as not to articulate, 

 although they are separated by a suture in the first two mentioned. 

 The males of the family Dajid* also have the head fused with the first 

 free segment of the thorax. 



Still a third thoracic segment, oi- what is usuallv the second free 

 segment, is united with the head in onh' one genus, the genus Sphy- 

 rajyus Norman and Steb])ing. 



1. Eyes. — The eyes, when present, are always paired. The}' may 

 be small and simple and situated some distance apart, or the}^ may be 

 largo, composite e3'es, formed of numerous ocelli and so close as to 

 be contiguous. Except in the Tanaidie, where the eyes are placed on 

 stalks, which are, however, never movable, they are invariably ses- 

 sile. The ocular lobes in the Apseiidida} are spine-like projections of 

 the carapace upon which the eyes are situated. 



Eyes are wanting in the following Isopod genera: Typhlotanais Sars, 

 L('2>fn(/)}atJila Sars, Tanaclhi Norman and Ste])l)ing, Sti^ongylura Sars, 

 CryptocopeSnYa, ILipJocope Sars, Aniiiihrura Sars, Ci^cidotea Packard, 

 Oh'olanides Benedict, Syscenus Harger, Phttyarfhrus Brandt, Tita- 

 nefhrst Schid'dte, Tiinaopxis Sars, Odathura Norman and Stebbing 

 (e^'es imperfectl}' developed or wanting), Lcptunthura Sars, Alaotanaia 

 Norman and Stebbing (there are minute ocular lobes bat no eyes) 

 Pseudotanais Sars (e3'es ari^ imperfect or absent), Amiropus Beddard, 



