DESCRIPTION OF THE GENUS. 



Serolis, Leach. 



Oniscus, Fabricius, Mantissa Tnsectoram, p. 240, 1787. In Part. 

 Asellus, Olivier, Encycl. M6th., t. i. p. 2.52. In Part. 



CymotJwa, Fabricius, Entomol. Syst., ii. p. 503, 1793. In Part. 

 Serolis, Leach, Diet. d. Sci. Nat., t. xvii. p. 340, 1825. 

 Brongniartia, Eights, Trans. Alb. Inst., ii. p. 53, 1833. 



Definition.— Qodj much depressed, round or oval in form, usually furnished with 

 long sickle-shaped epimera. Cephalic shield broad, terminating anteriorly in a short 

 median rostrum, uniting with fii'st two segments of thorax to form a cephalothorax. 

 Terminal segment of thorax rudimentary, its tergum unrepresented ; sternum partially 

 fused with that of preceding segment ; epimera absent. Abdomen consisting of three free 

 segments and a caudal shield ; first segment devoid of epimera, and completely enclosed by 

 the preceding and succeeding segments ; second and third segments with longer or shorter 

 epimera. Caudal shield usually pentagonal, with one or more longitudinal carinse, rarely 

 smooth. First pair of antennae subequal in length to second pair, the former with four 

 basal joints and a multiarticulate flagellum, the latter with five basal joints and a multi- 

 articulate flagellum. Mandibles stout and strong, with a long three-jointed j^alp. Maxillai 

 small and delicate. Maxillipedes large and operculiform, entirely covering maxillae. 

 Ambulatory appendages seven 23airs ; anterior pair (in male second pair also) modified 

 into a prehensile organ, the terminal joint folding back upon the greatly dilated pen- 

 ultimate joint ; last thoracic appendage smaller than the others ; first three pairs of 

 abdominal appendages natatory, with broad basal and two expanded distal joints fringed 

 with long plumose hairs ; inner joint of second pair prolonged in the male into a 

 penial filament ; fourth and fifth appendages branchial ; sixth pair natatory, compata- 

 tively small. 



External Characters. — The depressed form of the body which characterises the family 

 of the Isopoda as contrasted with the Amphipoda is very marked in the genus Serolis ; in 

 some .species (Serolis schythei, Serolis comuta, &c.) the body is almost flat ; in others 

 again {Serolis convexa, &c.) the convexity of the dorsal surface is greater, and Serolis 



