BY GEO. M. THOMSON, P.L.S, 61 



the carpus, and the tubercular projection of the meros are 

 protected by a few small spines. In the Mt. Wellington 

 specimens, on the other hand, the flanges on the carpus are 

 thinner and more flattened ; the meral projection is also flange- 

 like and rounded, and the whole limb is almost destitute of 

 hairs. The joereiojjoda are generally simpler and less spinous 

 in the Tasmanian than in the N.S. Wales form. The branchiae 

 of the ^/if/i pair in the males (fig. 7) are peculiarly modified. 

 I cannot find any reference to this structure in any other of 

 the Orchestidae, and would provisionally suggest that they serve 

 as a sort of clasping organ to assist in copulation. In the 

 largest specimen examined they were curled up, instead of being 

 somewhat flattened, as they appear in the figure. I am not 

 sure, also, whether they are equally developed on both sides of 

 the body. The pleopoda are reduced to a very rudimentary 

 condition. The first pair (fig. 8) have both branches developed, 

 but they are small and feeble, and the setae are extremely 

 slender ; the second pair are still smaller and more feeble, 

 "while I have failed to find the third pair at all in those speci- 

 mens examined. This defective condition is probably due to 

 the terrestrial habits of these Crustacea, as in aquatic Amphi- 

 pods these appendages serve as swimmerets, and aid the animal 

 in forward progression. In terrestrial forms this function 

 being no longer required, the necessity for the organ ceases, 

 and it has accordingly retrograded in its development. The 

 three pairs ofuropoda (posterior pleopoda of most authors) are 

 much as figured in Haswell's original paper (Proc. Linn. Soc. 

 N.S.W., vol. iv., pi. vii., fig. 1) the ante-penultimate pair being 

 much the longest, and reaching furthest back. The telson 

 (fig. 9) appears to me to be quite entire, rounded at the 

 extremity, and furnished with three small spines on each side. 

 There is a delicate longitudinal median line visible with a high 

 power, but this is due to the paired organs underneath showing 

 "up through its semi-transparent substance. I can detect no 

 trace of cleavage of the organ. Close underneath it lie the 

 very short ultimate tiropoda (fig. 10) with their conical terminal 

 joint, ending in a single spine. Looking at the telson from 

 above, the extremities of these appendages slightly protrude, 

 and this, probably, led Prof. Haswell to conclude that the 

 telson was ''cleft in the middle line posteriorly." 



The specimens found by me were yellowish or yellowish- 

 brown in colour. The largest was -^^ inch (or 10 mm.) in 

 length. 



16. Talorchestia diemenensis. Haswell (PI. v., figs. 6-8.) 



This species is relegated to the genus Orchestia by the Eev. 

 T. T. Stebbing (Ann. & Mag. of Nat. Hist., Oct. 1891, p. 325) 

 " — " Since both the figure and the description show that the 



E 



