128 THE VOYAGE OF H.M.S. CHALLENGER. 



dredged by the Challenger, the main difference between the two species is in the greater 

 elongation of the middle thoracic segments of L( j j>t<>gn<i/Iti<< australis, and in the absence 

 of serrations on the distal joints of the chelipedes. These differences, as wel] as others 

 which will be referred to in the course of the following description, seem to me to be 

 sufficient to distinguish the species. 



Leptognathia australis as already mentioned is represented in the Challenger 

 collection by a single specimen, an ovigerous female ; it measures about 4 mm. in extreme 

 length. 



The body is extremely narrow and elongated, the proportions between the 

 cephalothorax, thorax, and abdomen are as follows : — Cephalothorax 6, thorax 19, 

 abdomen 8 ; the proportions of Leptognathia longiremis, measured from Sara's figure 

 (pi. vii. fig. 18), are 5, 16, 8 ; it is evident, therefore, that in Leptognathia australis 

 the thoracic region comprising the free thoracic segments is proportionately longer 

 than in the other species. 



The cephalothorax is longer than the first free segment of the thorax, but not as long 

 as the first two segments taken together ; as the single specimen was mounted on a slide 

 so as to be seen from the side, I am unable to describe the shape of the cephalothorax ; 

 eyes are, however, completely absent. 



The first segment of the thorax is shorter than any of the following three, which are 

 subecmal and about half again as long as the first segment ; the fifth segment is shorter 

 than the fourth, but a little longer than the first ; the last segment of the thorax is 

 shorter than any of the others, with the exception of the first, which it equals in length. 

 The thoracic segments are separated from each other by well-marked constrictions. 



The point of insertion of the ambulatory appendages apj)ears to be characteristic in 

 many Tanaids ; in the present species the first pair are articulated close to the anterior 

 extremity of their segment ; the second, third, and fourth pairs at about the middle of 

 their respective segments; the two last pairs are articulated a very little nearer to the 

 posterior margin of their segments, the last a little more than the first, but still roughly 

 in the middle of the segment, not definitely at its posterior extremity as in Typhlo- 

 tanais lerguelenensis. The ovigerous lamellse are developed along the thorax as in 

 other species. 



The abdomen is altogether about as long as the two last segments of the thorax and 

 one-half the fourth segment ; the terminal segment is rather longer than the two preced- 

 ing, and ends in an obtuse rounded extremity. 



The antennules are not so long as the cephalo-thoracie shield, they are four-jointed, 

 the joints decreasing progressively in width as well as in length. 



The antenna! are of about the same length as the antennules; this structure is 

 entirely similar to that of the same appendage in Paratanais. 



The chelipedes are stout and robust in structure ; the first joint is the longest, with 





