new and rare Crustacea from Scotland. o4 
Posterior antenne three-jointed, second and third joints elon- 
gate and subequal, the first short, about half as long as the 
second; secondary branch very small, one-jointed, and arti- 
culated to the lower distal end of the first joint of the primary 
branch. Mandibles narrow, cylindrical, armed with a few 
moderately long teeth ; basal portion of mandible-palp stout, 
somewhat dilated, and furnished with a small one-jointed 
branch at the apex (fig. 4, Pl. VI.). Posterior foot-jaws 
small, the first two joints moderately stout, the last very 
small and forming the base of a slender and comparatively 
short claw (fig. 26, Pl. V.). The first pair of swimming-feet 
resemble those of Mesochra Lilljeborgit, Boeck, except that 
the end joints of the inner branches are proportionally longer, 
being equal to about half the length of the first joint (fig. 5, 
Pl. VI.). Outer branches of the second, third, and fourth 
pairs elongate; inner branches short, two-jointed (fig. 6, 
PI. VI.). Fifth pair foliaceous, small; the basal joints are 
subquadrangular, and their width equal to nearly twice the 
length ; but the slightly produced inner portion is triangular 
and furnished with two sete on the inner margin and one at 
the apex; secondary joints subquadrate, being nearly as 
broad as long, and bearing six sete, arranged at slightly 
irregular intervals round the outer margin and end; the 
second seta, counting from the inside, is much longer than 
any of the others (fig. 7, Pl. VI.). Caudal stylets short, 
length rather greater than the width, each provided with 
several sete, the principal seta being equal to nearly three 
fourths of the length of the animal. 
No males of this species were observed. 
Habitat. In pools near low-water mark on the shore at 
Musselburgh, Firth of Forth ; not uncommon, 
temarks. This very slender Copepod does not resemble a 
typical Mesochra, but from its general form seems rather to 
belong to that peculiar group represented by Cylindropsyllus 
and Leptopsyllus. In the structure of its various appendages, 
however, it is a true Mesochra. ‘The first pair of swimming- 
feet closely resemble those of Mesochra Lilljeborgii, differing 
only in the proportionally greater length of the end-joint of 
the inner branches. The small clawed posterior fovt-jaws 
and the peculiar form of the fifth pair of thoracic feet are, 
however, very good and distinct specific characters, inde- 
pendent of the elongate and slender form of the animal. 
The species is named in compliment to Prof. W. C. 
M‘Intosh, the Scientific Director of the Fishery Board for 
Scotland. 
