ISOPODS WITH FINGER AND THUMB 319 
stance that the heart occupies the earlier segments of the 
perzeon, whereas in those Isopoda which have branchial 
pleopods, the heart is correspondingly situated in and 
near the pleon. ‘The tribal name refers to the fact that 
the first pair of trunk-limbs, or gnathopods (corresponding 
to the second maxillipeds of preceding descriptions), are 
furnished with a chela, the two terminal joints forming an 
opposed thumb and finger as in the familiar chelipeds of 
crabs and lobsters, a character not met with in the rest of 
the Isopoda. The uropods are slender, the branches often 
flagelliform. ‘The eggs are carried in a marsupium of thin 
plates, which either form one pair attached to the fourth 
free segment alone, or four pairs attached to four segments. 
The tribe includes only two families, the Apseudidee 
and T'anaidze, distinguishable by numerous characters both 
external and internal. 
Family 1.—Apseudide. 
The body is depressed, the carapace generally having 
a well-developed rostrum and carinate sides, with pyriform 
or spine-like ocular lobes. The segments of the pleon are 
well defined, narrower than those of the perzon. 
The first antennz, placed at the front corners of the 
carapace, are remarkable in this sub-order by having two 
many-jointed flagella. The second antenne with the 
bases contiguous are placed between and below the first, 
and are often furnished with an articulated scale, ciliated 
all round. The flagellum is many-jointed. 
The mandibles have a three-jointed ‘palp.. The first 
maxille have two incisive lobes and a two-jointed back- 
ward-directed ‘ palp,’ ending in two or more sete. The 
second maxille are furnished with sete and spines. The 
maxillipeds have a large laminar epipod, branchial in 
function. The first gnathopods are strong and chelate, 
the inner margins of the finger and thumb being usually 
tuberculate in the male and serrate in the female. The 
second gnathopods are fossorial, having the last three 
joints, especially the penultimate or ‘hand,’ flattened, the 
