34 
W. M. TATTERSALL. 
Endopods of the third thoracic limbs (Fig. 10) with the merus longer than the 
tarsus; latter composed of six joints ; nail well developed and longer than the last 
joint of the tarsus. 
Endopods of the remaining thoracic limbs become successively longer and more 
slender from the fourth to the eighth ; the increase in length takes place chiefly in 
the ischial joint; the number of joints in the tarsus of the endopods also increases 
in the more posterior limbs ; in one specimen there were six joints in the tarsus of 
the third limb, six in the tarsus of the fourth, ten in the tarsus of the seventh, and 
twelve in the tarsus of the last limb. 
Genital appendix (Fig. 11) on the last thoracic limb of the male exceedingly 
long and slender, equal in length to the first three joints of the limb to which it is 
attached. 
Pleopods (Fig. 12) similar in both sexes, consisting of a single ramus bearing 
proximally and externally a rather large process tipped with setse. 
Telson (Fig. 13) a little longer than the last segment of the pleon, and more 
than twice as long as broad at its base ; cleft at the apex for nearly a quarter of its 
length, cleft rather wide, its margins armed with about eighteen teeth on each side ; 
the apex of each lobe of the cleft armed with a pair of spines, the inner one the 
shorter; lateral margins armed throughout their whole length with about seventy 
spines, which become arranged in series towards the apex. 
Inner uropods slightly longer than the telson, with a row of moderately slender 
and long spines on its inner ventral margin, varying in number from twenty-six to 
twenty-eight, and extending from the otocyst to near the apex ; spines not arranged in 
series, but increasing in size distally. In some specimens the spines extend further 
down the uropod than in others. 
Outer uropods about half as long again as the inner. 
Length, of an adult female with embryos in the brood pouch, 21 mm. ; of an 
apparently adult male, 25 mm. A second female with embryos in the brood pouch 
measured 23 mm. 
It is not a little interesting that this genus should have been discovered almost 
simultaneously in the northern and southern hemispheres, M. farrani, Holt and 
Tattersall (1906 (2)) having just been described when the ‘Discovery’ collections 
came to hand. 
M. posthon is a more stoutly built form than M. farrani, and is further 
distinguished from the latter in the following characters : — 
Antennules. — M. farrani has not the outer corner of the basal joint of the 
peduncle produced nearly as much as in M. posthon. 
Thoracic limbs .— The tarsus of the endopods in M. posthon is composed ol six to 
twelve joints, while in M. farrani there are only four. 
Genital appendix to the last thoracic limb of the male is much longer and more 
slender in M. posthon than in M. farrani. 
