ISOPODA. 101 



smallness seems to forbid all possibility of copulation; according to 

 Desmarest it is provided with two eyes; its body is straight and al- 

 most linear. 



These Crustacea form but a single subgenus, that of 



Bopyrus, Lat., 



The most common species is the Bopyrus crangorum, Lat., 

 Gener. Crust, et Insect., I, 114; Monoculus crangorum, Fab.; 

 Fouger. de Bondar, Mem. de l'Acad. Roy. des Sc, 1772, pi. l'j 

 Desmar., Consid. XLIX, 8 13. It lives on the Palaemon ser- 

 ratus, and the Pal. squilla, placed directly on the branchiae and 

 under the shell; it occasions a tumour on one of its sides, re- 

 sembling a wen. The fishermen of the British channel con- 

 sider them as very young Soles or Plaice. 



A second species, the B. des palemons, has been described by 



Risso, under the female of which he observed eight or nine 



hundred living young ones(l). 



The second section CYMOTHOADA,Lat. comprises Isopoda with 



four very apparent setaceous antennae, almost universally terminated 



by a pluri-articulated stem; having eyes, a mouth composed as 



usual(2); vesicular branchiae arranged longitudinally and in pairs; 



the tail formed of from four to six segments, with a fin on each side 



near the end; and the anterior feet usually terminated by a small 



stout nail or claw. They are all parasitical. 



The eyes are sometimes placed on tubercles on the top of the 

 head; the tail consists of but four segments. 



Serolis, Leach. 



But a single species is known, the Cymothoa paradoxa, Fab. 

 The antennae are placed on two lines, and terminated by a pluri- 

 articulated stem. Under the three first segments of the tail, 

 between the usual appendages, there are three others, trans- 

 versal and terminated posteriorly in a point(3). 

 Sometimes the eyes are lateral and not placed on tubercles; the 

 tail is composed of five or six segments. 



Here the organ of sight is not formed of smooth, granular, ap- 

 proximated eyes; the antennae are placed on two lines, and consist of 

 seven joints at least; the six anterior feet are usually terminated by 

 a small, stout nail. 



(1) See the work of Desmarest, who has completely described this subgenus. 



(2) See our general observations on the Malacostraca with sessile eyes. 



(3) For other details consult Desmar., Consid., p. 2y2 294. 



