GENERA CUM A, ALAUNA, AND EODOTRIA. 327 



are almost as long as the foot-jaw itself, arise from the middle part of this seg- 

 ment ; the external spine is free of spinules altogether, but the internal is 

 armed, on its external edge only, with a great number of articulated spinules. 

 The second segment of this footjaw is very bhort, and its posterior edge bears 

 two very short articulated spines of equal length ; these spines are spiniferous. 

 The third segment is almost equal in length to the first, and, like the second, 

 also gives rise to nine or ten articulated and spiniferous spines. The fourth 

 segment is small and rounded, being also armed on its posterior edge with sim- 

 ple spines. The fifth segment is thumb-like, and spinous on its posterior edge. 



The external pair of footjaws are much larger than the internal ; they are five- 

 jointed, and are armed in the same way as the first pair, except that the ex- 

 ternal edge of the first segment is armed at regular intervals with small tufts 

 of very fine hairs ; the extremity of the second segment is also armed with a 

 very long articulated and spiniferous spine. These two extremities just de- 

 scribed are in general lying in such a way as to cover the organs of the 

 mouth. 



The first two pairs of legs are constantly concealed beneath the carapace when the 

 animal is at rest, covering the footjaws and the organs of the mouth, and appear 

 only to be used when the animal is swimming. The anterior or ambulatory 

 division is five-jointed ; the first joint is about twice the length of all the others 

 combined ; it is considerably bent and very broad ; its internal edge is armed 

 at regular intervals with pennicillated tufts of hair ; the three following seg- 

 ments are quite free of spines, but the last is anned at its extremity with a 

 strong claw and two smaller spines. An articulated thumb-like and chelate 

 joint arises from the extremity of the first segment, immediately internal 

 to the last four segments. The natatory or posterior division of this leg is 

 multiarticulate ; the first two segments are longest, being equal in length to 

 the first segment of the anterior division ; the remaining segments are mi- 

 nute, about nine or ten in number, each of which gives off a very long spiniferous 

 setum, which is articulated at its distal half. The second thoracic leg of this 

 species presents to us one of those beautiful and delicate structures which it is 

 impossible either to describe or to delineate with even a remote degree of accu- 

 racy. The ambulatory division is very long and slender, six -jointed ; the first 

 joint is long and very much flattened, but tapers from the middle towards its 

 distal extremity, which is armed with a very long and pointed spine ; the fol- 

 lowing joints are all equal to one another in length, except the last, which is 

 minute. The natatory division of this leg is seven- or eight-jointed, and is 

 equal in length to the first segment of the other division. The last five seg- 

 ments are all armed with long articulated and spiniferous setae, which smaller 

 spines are again spinulose. The four following pairs of legs are simple, that 

 is, they are merely ambulatory ; they are all six-jointed, and are very spiny 4 

 The segments of the body from which they arise are all ovoid, their dorsal edge 

 being sharp and pointed. 



The abdominal portion of the body is long and slender, seven-jointed and moni- 

 liform ; the last joint is minute, and lies between the caudal styles which arise 

 from the extremity of the sixth segment ; these styles are of no great length 

 in this species ; they are composed of three parts ; each style consists of a 



