ISOPODA. 
29 
appendages are lost; they are, however, uninjured in the smaller specimen. The first 
appendage of this series, the second of the mesosome, 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 setse, 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 setae 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 setm fringe these joints throughout. 
The exopodite is a delicate semicircular structure fringed with fine setae, and on 
its curved border with long plumose setae. 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 setae. 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. 
