158 ANTHURIDA. 
tudinally, but, in the first pair alone, the outer division 
is very much narrower than the inner division. The 
terminal pair of tail-feet are transformed into a pair of 
crustaceous plates, affixed to each side of the penultimate 
segment at its base; the inner plates have a transverse 
articulation beyond the middle,* and the outer plate 
is affixed vertically and falls back, when at rest, upon 
the dorsum of the terminal joint, fitting into the de- 
pression formed by the transverse carina on that segment. 
The lower figure, P z, in page 160, represents the lateral 
view of the tail of A. gracilis, being the four basal seg- 
ments (represented as entirely soldered into one joint), 
beneath which is seen three pairs of tail-feet in a mass, 
the long appendage arising from the lower anterior angle 
of the segment representing the anterior large pair that 
covers the rest as an operculum; the fifth segment of 
the tail is also shown as distinct, followed ‘by the large 
laterally-deflexed portion of the terminal pair of tail-feet 
or scales which it supports; the articulated extremity of 
the two inner divisions of this pair of appendages, and 
the truncate extremity of the middle portion of the tail 
being also shown in the deflexed portion of the figure. 
The left-hand figure, P’, represents the ventral surface 
of the two terminal segments of the body, and of the tail, 
showing the inner division of the anterior pair of tail- 
feet, concealing the outer division of the same pair as 
well as the whole of the remaining pairs of the organs. 
Fig. p represents the outer division of the left-hand pair 
of the first respiratory tail-feet, and fig. p’, a portion 
of its lateral, deeply ciliated margins, showing the in- 
sertion of the cilia. 
The anterior pair of feet are strong but short, not 
* In 4a this articulation is oblique, and extends to the insertion of the 
outer plate. 
