868 ARCTURIDA. 
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 ciliz, 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 ciliz, 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- 
