158 ANTHDRID^. 



t'udinally, but, in the first pair alone, tlie 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 r, 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. /»", a portion 

 of its lateral, deeply ciliated margins, showing the in- 

 sertion of the cilise. 



The anterior pair of feet are strong but short, not 



* In ^ga this articulation is oblique, and extends to tlie insertion of the 

 outer plate. 



