new and rare Crustacea from Scotland. 52 
Habitat. In pools near low-water mark on the shore at 
Musselburgh, Firth of Forth ; not uncommon. 
Remarks. This may be distinguished from any other species 
of Leptopsyllus known to us by the structure of the anterior 
antenne and of the fourth and fifth pairs of thoracic feet. 
Mesochra spinicauda, sp.n. (PI. V. figs. 12-25.) 
Description of the Species—Female. Length °58 millim. 
(75 of an inch). Body elongate, cylindrical, slender. Ante- 
rior antenne 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 ............ PPL a OGY | 
The first joint of the posterior antenne 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 tew 
marginal and terminal sete (fig. 16). he armature of the 
maxilla somewhat resembles that of the mandible, and the 
maxilla-palp is a narrow cylindrical process furnished with a 
few sete 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 smail and forming the base of 
long slender claws (fig. 19). Inner branches ot 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 1s about twice the length of the second, while 
the second and third are nearly ot equal length (tig. 20). 
The second, third, and fourth pairs are slender and elongate ; 
the inner branches of the tourth 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 
apart on the inner margin, wlule the outer margin is partly 
fringed with small sete (fig. 21). Fitth 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 setilorm 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 
