ANTHURA GRACILIS. 161 



THIS species is well defined by the strong, raised, 

 lateral margins to the segments of the body and tail, 

 by the consolidation of the basal segments of the latter 

 almost into a solid mass, the articulations being, how- 

 ever, clearly indicated by impressions on the under edge 

 of the lateral margin, and especially by the characters 

 of the terminal segment of the tail and its appendages, 

 noticed in the specific characters given above. It is, 

 however, rather difficult to describe precisely the curious 

 construction of this terminal portion of the body. 

 Montagu says that " the body is terminated by 

 five large caudal appendages truncated at their ends, 

 these are deflected nearly at right-angles with the body, 

 the middle one fixed, and the lateral ones jointed and 

 spread a little upwards in a semicircular form." The last 

 term is not, however, at all expressive, and should, 

 doubtless, have been " semi cylindrical," since the ap- 

 paratus, when open, forms a concave cup-like disc, and 

 when at rest, from being affixed vertically, the outer 

 plate falls back and shuts down upon the dorsum of the 

 middle tail-plate, like the two wings of a closed triptych. 

 The irregularly crenulated margin of the extremity of 

 these caudal plates also affords another distinctive cha- 

 racter. Not having seen fresh specimens of this species, 

 we are unable to give a more precise description of the 

 antennae than is conveyed in our generic observations. 



The fore legs, although not longer than the succeeding 

 pairs, are very much more robust, with a large, elongate- 

 ovate hand, the upper basal angle being swollen, and the 

 palm having a deep incision along its outer half (which 

 we believe to be caused by the elongation of the outer 

 and lower angle of the preceding joint) which is slightly 

 rugose. The other legs are much more slender, with the 

 joints of nearly equal length, the fifth and sixth having 



VOL. II. M 



