l76 transactions. — Zoology. 



basal one broader and longer than the terminal one. The ends of both 

 branches supplied with numerous rather long sets. Telson squamiform, 

 sides arched, ending in a blunt point tipped with a few short setse. Colour 

 transparent. Length of largest specimen -46 inch. 



Hab. Pump at Eyreton. 



As this Isopod is exceedingly interesting, I have endeavoured to describe 

 and figure it in some detail. The mouth parts are all small and exceedingly 

 difficult to make out, owing to the various parts being to a considerable 

 extent anchylosed together ; and I have to thank Professor Hutton for 

 valuable aid in their dissection. Though I have by his aid succeeded in 

 making out the various parts which form the mouth, I cannot, in the absence 

 of sufficient books of reference, be quite certain of their homologies. All 

 the parts of the mouth project forwards ; just below the antenna there is a 

 strong moderately sharp labrum or upper lip (pi. X,, fig. 3). The appendage 

 which, by its position, should correspond to the mandibles does not appear 

 to perform the function of mandibles. The two parts, right and left, appear 

 to be here anchylosed together, and no trace of any palp is to be seen ; the 

 distal ends are fringed with very short indistinct setse, and the opposite end 

 is notched (fig. 4). The first maxilla is simple, spoon-shaped at the end, 

 which is fringed with set© (fig. 5). The second maxilla is also simple, 

 straight, and towards the end it is supplied with short teeth (fig. 6). Though 

 this appendage, by its position, appears to correspond to the second maxilla, 

 yet it is the only one that looks at all like a masticatory organ. If the right 

 and left halves were rubbed longitudinally together they would, owing to the 

 short teeth at their ends, form a most efficient triturating organ. The most 

 posterior of the mouth organs, the maxillipedes (fig 7), are somewhat concave 

 and operculiform, enclosing the rest of the mouth parts. The basal parts of 

 the two halves on the two sides are anchylosed together, and to the head 

 itself, but the terminal portions are free, and the ends, which are at some 

 distance apart, are tipped with setse. On each side, near the middle, is a 

 peculiar looking small round piece, which is articulated to the rest of the 

 limb. This may possibly represent a rudimentary exopodite, while the free 

 terminal portion may be the endopodite of the typical Crustacean limb. 



The appendages of the abdomen on each side consist of a short basal 

 joint supporting two more or less oval branchial plates (fig. 12). In the 

 appendages of the first abdominal segment the outer branch is much 

 enlarged and forms an operculum over the branchial plates ; the inner 

 branch, which hes under the operculum, is narrow (fig. 11). In the view of 

 the abdomen from below (fig. 10), the two halves of the operculum have 

 been slightly separated from one another to show the branchial plates 

 underneath. 



