74 Mr. Westwood on ^rcturus, 



dric in the males, in which sex it is without any orifice or inferior 

 lamellae, and is the narrowest part of the body ; but in the females 

 it is as wide as the head, and furnished beneath with two thin mem- 

 branaceous plates lapping oA'er each other, and serving as an en- 

 velope for the eggs. 



The fourth pair of legs is attached at tlie anterior angles of this 

 segment beneath. 



The three following segments of the body (terminating the tho- 

 racic portion) are short, rounded at the sides, and respectively fur- 

 nished with a pair of strong legs, evidently formed for prehension, 

 having the last joint terminated by a bifid hook. These legs are not 

 ciliated. 



There are only two apparent remaining segments, of which the 

 first resembles the preceding, and is furnished beneath with a pair 

 of long thin plates, which are articulated to this joint and the fol- 

 lowing at the outer edge, and are capable of shutting and opening 

 like a pair of cupboard- doors. They are terminated by a slender 

 acuminate process. On opening this pair of organs a most beau- 

 tiful apparatus, consisting of no less than twenty-two distinct instru- 

 ments, is exhibited, and which, under a magnifier of high power, 

 presents the most elegant appearance. 



At the base (in the male at least) is a pair of minute organs, ter- 

 minated by two somewhat cultrate plates, and which are probably 

 connected with the office of generation. The first double pair of 

 subabdominal respiratory plates (which cover all the rest) succeed 

 these, each of which is composed of a rather long and bent flat foot- 

 stalk, having on the outside four curious bent ciliated setae, and ter- 

 minated by two long plates of a very delicate texture, and slightly 

 scolloped at the extremity in a double series for the insertion of the 

 cilise, which are very long and beautifully bearded : the base of the 

 internal plate is also furnished with several long bearded setae. 



The second double pair of these organs is nearly similar, except 

 that the basal portion is shorter and one of the plates is much nar- 

 rowed. 



The third double pair is very diiFerent, being composed of a very 

 short footstalk and two large oblong-oval plates, one of which is 

 plain on its margins, whilst the other is setose at the extremity, and 

 is notched on the outside for the insertion of two longer bearded 

 setae. 



The fourth and fifth pairs of these organs are also double, and like 

 the third pair, except that the outer plate is not ciliated, and is fur- 

 nished with a single plain seta at its outer margin. 



The terminal segment of the body is large, convex, and tenninated 



