368 ARCTURI13.E. 



above, the first of these segments appears divided into 

 two, the posterior lateral angles being produced into 

 distinct pointed lobes : there is also a much less distinct 

 impression across the middle at the lower sides. The 

 terminal segment, also, has each side produced in the 

 middle into an acute angle, behind which the apex is 

 gradually acuminated. 



The first segment of the tail is furnished beneath with 

 a pair of long thin plates, articulated to this and the 

 following joint at the outer edge, and which are capable 

 of shutting and opening like a pair of cupboard doors. 

 Each of them is terminated by a slender acuminated 

 process. On opening this pair of organs a most beautiful 

 apparatus is exhibited, consisting of no less than twenty 

 distinct pieces, arranged in five double pairs, serving for 

 respiration. At the base (in the male at least) is also 

 a pair of minute organs, terminated by two somewhat 

 cultrate plates. The first double pair of the respiratory 

 plates (which cover all the rest) succeed these appen- 

 dages, and are composed of a rather long and bent 

 flat foot-stalk, having on the outside four curiously bent 

 ciliated spines, and terminated by two long, delicate, 

 membranous, equal-sized plates, slightly scalloped at the 

 extremity for the insertion of the cilia3, which are very 

 long and beautifully bearded ; the base of the internal 

 plate is also furnished, on the outside with several long 

 bearded spines. The second double pair of plates are 

 nearly similar to the preceding, except that one of the 

 plates is very much narrowed. The three succeeding 

 double pairs of plates are much smaller and shorter, each 

 consisting of a pair of oval membranous plates, almost 

 destitute of cilise, attached to a short basal foot-stalk. 



Detailed representations of most of the organs above 

 described will be found in the first volume of the " Trans- 



