40 
BULLETIN OF THE LABORATORIES 
The size varies greatly, a full grown female with eggs in the brood 
cavity is nearly .90 mm. long and .70 high, while a smaller female 
measures .65 mm. long by .44 high. The form of the shell is nearest 
like that of I. acutifrons, the heighth being less than in /. sordidus, 
and the angle between the ventral and posterior margins less than in 
1 . agilis. The entire length of the post-abdomen in the large female 
is .56 mm. measured to the base of the caudal stylets, of which length 
.168 mm. pertains to the claws. The width of the post- abdomen is 
but. 14 mm. Thus it is evident that the proportions of the post- 
abdomen differ greatly from any of the other species, it being very long 
and narrow. The terminal claws are exactly as in /. agilis^ having 
two small basal spines and a few sharp serrations near the apex, an- 
teriorly. Near the base of the claw is a cluster of small spines of 
two sizes, then begins a series of about sixteen lateral teeth averaging 
.02 mm. in length and extending to the sides of the anus. Above 
this point the contour of the margin is convex and is ornamented with 
nine spines twice as long as the preceeding. Then follow the promi- 
nences which bear the long and simple caudal setae. Besides the 
above mentioned spines there are four spines on either side upon the 
lower posterior angle of the post-abdomen which are four times as long 
as those of the previously mentioned continuous series (/. e. . 08 mm. ) 
Above, the abdomen is hirsute or thorny as in /. agilis^ and the process 
for closing the brood sac is similar. It will be seen that the post- 
abdomen differs in armature as much as in form from other species. 
From I. sordidus it differs in the following points : — the claws are not 
pectinate behind but are serrate in front, the anal opening is higher 
and the details of the spines vary ; from /. acutifrons it differs in that 
the claws are not pectinate, neither is there a spine in front of the claws, 
and the anus is not terminal ; from I. agilis it differs, in that the shape 
is different, there are fewer enlarged spines, and the shape of the nine 
spines above the anus is different. The head is convex, resembling 
/. so 7 'didiis most nearly, but the antennules are much longer and more 
slender than in any other known species. They are .17 long and about 
.016 mm. wide, while the longest seta is .084 long. The antennae are 
almost exactly as in /. so 7 'didiis. The labrum has the usual shape, as 
have the jaws and other appendages. The margins of the shell are 
ornamented with spines simply pectinate or barbed, as in /. agilis. In 
/. sordidus these spines are variously branched and in that form alone 
of the European species, according to Kurz, is there a failure to per- 
