62 Messrs. T. and A. Scolt on some 



Habitat. In jiools near low-water mark on tlie shore at 

 WusselbnrLrh, Firth of Forth ; not uncommon. 



Bemarks. This may be distinguished from any otlicr species 

 of Leptojisylhis known to us by the structure of the anterior 

 antcnnie and of the fourth and fifth pairs of thoracic feet. 



Mesochra spinicauda, sp. n. (PL V. figs. 12-25.) 



Description of the Species. — Female. Length '5S millim. 

 (^ of an inch) . Body elongate, cylindrical, slender. Ante- 

 rior antennaj slender, rather longer than the first cephalo- 

 thoracic segment, seven-jointed ; the second joint much 

 longer and "the fifth shorter than the others. The formula 

 shows the proportional lengths of all the joints — 



Proportional lengths of the joints 



6 . 20 . 6 . 8 . 4 . 8 . 11 



Number of the joints 1 2 3 4 5 6 7 



The first joint of the posterior antennae is short, the second 

 elongate and nearly twice the length of the last joint ; second- 

 ary branch very small, articulated to the lower proximal 

 half of the second joint (fig. 15). The mandible-palp consists 

 of a single moderately long narrow joint, which bears a few 

 marginal and terminal set^ (fig. 16). The armature of the 

 maxilla somewhat resembles that of the mandible, and the 

 maxilla-palp is a narrow cylindrical process furnished with a 

 few setee at its truncate apex and bearing a small lateral lobe, 

 ■which forms the base of a slender hair. Posterior foot-jaws 

 large ; terminal joints very small and forming the base of 

 long slender claws (fig. 19). Inner branches of the first pair 

 of swimming-feet somewhat longer than the outer branches 

 and composed of two nearly equal joints ; the first joint of the 

 outer branches is about twice the length of the second, while 

 the second and third are nearly of equal length (fig. 20). 

 The second, third, and fourth pairs are slender and elongate; 

 the inner branches of the fourth pair, which, like those of the 

 preceding pairs, are composed of two nearly equal joints, 

 extend beyond the second joint of the outer branches, and 

 each of the joints bears two minute spines placed widely 

 a} art on the inner margin, while the outer margin is partly 

 fringed with small setae (fig. 21). Fifth pair foliaceous ; the 

 inner portion of the basal joints is produced into a subtrian- 

 gular lobe that extends slightly beyond the secondary joints, 

 and terminates in a stout setiform elongate spine; the inner 

 margin of the basal joints is also provided with a fringe of 

 minute hairs and with a slender seta near the apex; the outer 



