ISOPODA. 



29 



appendages are lost ; they are, however, uninjured in the smaller specimen. The first 

 appendage of this series, the second of the mesosomc, comprises six joints, the first of which 

 is large and stout, the rest progressively decrease in size, and all are liberally provided 

 with small arborescent chromatophores. The second joint has two serrations on its 

 outer or ventral side, at each of which are a few long setae, distally, both ventrally and 

 dorsally, but not laterally ; there is also a distal fringe of long setse ; the following joint 

 has a single serration, the next has three, and the setse connected therewith are 

 distinctly spinous ; the penultimate one has seven of these so-called serrations, but very 

 small at first, increasing in size distally ; the setse they bear are very small at first 

 but increase to long ones distally, on the opposite side of the joint the distal fringe is 

 long and spinous. The ventral margin is slightly expanded and flattened as a blade, 

 chiefly proximally. The sixth joint or dactylus is stout and capable of folding on the 

 preceding one in a subchelate manner. This appendage constitutes a secondary 

 sexual character in the adult animal where it becomes modified to form a prehensile 

 organ, and differs considerably from the remainder which are distinctly locomotive in 

 function. As such it is figured and very briefly described by Eights. For this species 

 or S. cornuta, neither Dr. Studer nor Mr. Beddard give any description of this 

 appendage as distinct from the others, though both refer to its modification generally 

 among members of the genus. From this and other circumstances as previously indicated 

 it may be assumed that their specimens were immature. The other thoracic appendages 

 are alike in structure, the propodal joint is slender and not in any way expanded, 

 nor does the dactylus appear capable of being reflexed upon it in a subchelate 

 manner. The spinous armature varies with the size of the limb or the joint where 

 it occurs, and the last appendage of the mesosome only differs from the others in size. 



Of the abdominal appendages the first three pairs are adapted for swimming. 

 The base of each limb is roughly in the form of a truncated cone directed towards the 

 middle line, and articulated to the sternum near one corner of the narrow base which 

 is curved outwards ; this angle bears three stout setse on the first and two on the 

 remaining appendages, other fine setse fringe these joints throughout. 



The exopodite is a delicate semicircular structure fringed with fine setse, and on 

 its curved border with long plumose setse. The endopodite is smaller and attached to 

 the protopodite at about two-thirds of its length ; this shows more distinctly a ribbed 

 structure, each rib corresponding to a long plumose setse. The three pair of appendages 

 do not differ materially in shape or structure except that the straight posterior border 

 is prolonged into the " penial filament." This is a slender rod-like body passing 

 towards the middle line, it then bends somewhat abruptly backwards, and is grooved 

 on its inner side. It is about 4'5 mm. long, and appears to be jointed at the bend; 

 but this is probably due to injury, as there is no trace of such a structure in the 

 smaller specimen where, moreover, this organ is very much smaller. This organ of 

 the larger specimen is very much smaller than -that indicated in Eights' figure. 

 In their description of S. cornuta neither Dr. Studer nor Mr. Beddard allude to it. 



