No.im NATURAL HISTORY OF THE ISOPODA — RICHARDSON. 9 



number of segments is found; first, in the Tanaidse, in the males of 

 the Dajida> and in the species CrahyzoK Jonglcd^idatus and Arcturides 

 cornutus^ where the first free segment is fused with the head; secondly, 

 in the Serolida% where the first free thoracic segment is united with the 

 head, the five following segments being free, the seventh segment, 

 however, difiering in this respect that it is represented onl}^ on the 

 ventral side by a short sternum, there ])eing )io indication of it on 

 the dorsal surface; thirdly, in the genus Sj>Jiyra2)w^ Norman and Steb- 

 bing, one of the Apseudida', where the first two free segments are 

 fused with the head; fourthly, in the genus hcJmosom-a Sars, where the 

 fourth and fifth segments are united to form a columnar center; and 

 finally in the females of the Gnathiida? where consolidation occurs in 

 the fourth, fifth, and sixth segments. 



In many Isopods the lateral parts of the segments are produced as 

 broad plates on either side of the body, these plates being often dis- 

 tinctly separated dorsally, with the exception of the first, from the 

 segments. They are the epimeral plates or coxopodites. These 

 epimera in many genera are firmly coalesced with the segments with 

 no sutures evident as an indication of their union. The epimera 

 of several segments may be fused with the segments, while those of 

 the following segments may be quite distinct. In many species of 

 JVerocila Leach the epimera are very long and greatlj' produced, as is 

 also true of all the deep-sea species of the Serolidge, especially in the 

 males, with the exception of S. antarctica Beddard. 



The segments of the thorax are more or less equal in length, the 

 greatest deviation in this respect occurring in the genus Astacilla Cor- 

 dinor and in the genus Ardurufi Latreille, where the fourth thoracic 

 segment attains great development, being elongated to such a degree 

 in Astacilla that it becomes equal to all the other six segments in 

 length. JVxsa Leach has the sixth segment of the thorax larger than 

 the others and produced backward in a bidentate process. IlasweUia 

 Miers, also a genus of the Spliffiromidte, has the last thoracic segment 

 produced in a broad plate or shield over and bej'ond the pleon. 



In (7(>/r/;^^A«<?'rt Richardson the last segment of the thorax is abruptlj^ 

 so small and short that it might easily be mistaken for the first abdom- 

 inal segment. Not only the last segment, but also the first, in the 

 Gnathiidte is very small, the last segment being hardly distinguishable 

 from the segments of the abdomen. 



1. Legs. — The legs are usually fourteen in number, arranged in 

 seven pairs, one pair for each of the seven thoracic segments. The 

 Gnathiida^ have but six pairs of these appendages, those of the last 

 segment being wanting. This is also true of the following genera of 

 Anthurida; Jfyssura Norman and Stebbing, Crurcgens Chilton, and 

 CoJanthura Richardson. The genus Uropodlas Richardson is unique 

 among the Armadilliida, and ITarpony,!' Sars among the Cymothoida% 

 in also lacking the appendages of the last thoracic segment. In all 



