DESCRIPTION OF THE GENUS. 



Serolis, Leacli. 



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

 Asellus, Olivier, Encycl. ^I6th., t. L p. 2.52. In Part. 



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

 Serolis, Leacli, Diet. d. Sci. Nat., t. xvii. p. 340, 182.5. 

 Bronijniartia, EigMs, Trans. Alb. Inst., ii. p. 53, 1833. 



Definition. — Body much depressed, round or oval iu form, usually furnished with 

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

 median rostrum, uniting with first 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 carin^e, rarely 

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

 basal joints and a multiarticulate tiagellum, the hitter with five basal joints and a multi- 

 articulate flagellum. Mandibles stout and strong, with a long three-jointed palp. Maxillne 

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

 Ambulatory appendages seven pairs ; 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 iu the male into a 

 penial filament ; fourth and fifth appendages l)rauchial ; sixth pair natatory, compara- 

 tively small. 



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

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

 some fi])ecies {Serolis schythei, Serolis coriiut<(, &e.) the body is almost flat; in others 

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



