FAMILY SPHAHROMIDA. 93 
pairs in various forms show numerous minor differences as to 
relative length and thickness of joints, equipment with hairs, 
etc., but the differences must be exhibited in figures. Three 
or four legs from the same side representing the essential 
deviations found between the pairs of the same animal ought 
to be selected for illustrations to be done with the same 
degree of enlargement; the same legs from the same half of 
different animals must be drawn so that if, for instance, the 
seventh left leg of one species is seen from below (from in 
front), this leg of all the other animals ought to be shown 
from the same side. The most interesting differences in the 
legs shall be enumerated here. In Amphoroidea typa 
(M.-Edw.) the three anterior pairs are slender, but especially 
the three following pairs exceedingly thick and short; in A. 
falcifer (Thoms), the difference is not so highly developed, 
but stillremarkable. In Spheroma (Bosc.) and Hemi- 
spheroma (n. gen.) the three anterior pairs are equipped with 
very long, stiff, plumose notatory setae on the outer side of 
some joints; this feature I have not observed in any other 
genus. In the three genera constituting the section Ancinini 
the first pair terminates in a robust prehensile hand, the sixth 
joint being much thickened, and the seventh with its claw 
folded back along the lower margin of the sixth, quite as in 
numerous Amphipoda. ‘The sexual difference found in the 
legsin Parasphzroma (Stebb.) and the genera constituting 
the sections Monolistrini and Ancinini are mentioned in the 
preceding chapter. 
The abdomen.—In Limnoria all six abdominal seg- 
ments are free and movable, in Plakarthrium all are fused 
with each other. But some difficulty is met with as to the 
Spheromine. In all forms of this sub-family (Vireia 
burgunda (Dollf.) and Ceecospheroma (Dollf.) excepted) 
the abdomen consists of two movable parts, and the question 
arises as to the number of segments constituting each part. 
But a comparison of the two posterior segments and the 
articulation between them in Limnoria with the structure in 
Spheroma gives the result that in the latter genus the 
