OF ’DENISON UNIVERSITY. 
41 
feet the moult; in our species, which has simply pectinate setae, the old 
coverings are all but uniformly retained. The spines of the lower 
posterior margin are from .16 mm. to .20 mm. long. 
Such are some of the chief peculiarities of the species, but, to make 
the relation between the four species of this little-known genus even 
clearer, if possible, the following comparative table is appended. 
The shell moulted periodically — 
/ /. agilis. 
\ I. acutifrons. 
The shell not moulted but retained — 
J /. sordidus. 
\ I. spinifer. 
Antenules not more than eight times as long as broad— 
f /. sordidus. 
J /. agilis. 
( I. acutifrons. 
Antenules more than eight times as long as broad — 
I. spinifer. 
Claw of post. abdomen pectinate — 
( /. sordidus . 
\ /. acutifrons. 
Claw of post-abdomen not pectinate — 
/ I. agilis. 
\ I. spinifer. 
A strong spine in front of claw — 
1. acutifrons. 
f I. sordidus. 
Fine bristles or none in front of claw 
■< I. agilis. 
( I. spinifer. 
Anus opening near the claws — 
I. acutifrons. 
f I. sordidus. 
Anus about midway of the posterior border — 
J I. agilis. 
( /. spinifer. 
Marginal spines of shell much branched — 
I. sordidus. 
C I. agilis. 
Marginal spines nowhere much branched — 
) I. acutifrons. 
( I. spinifer. 
Elongated anal spines on either side, four or five, very long — 
I. spinifer. 
f I. agilis. 
Elongated anal spines more numerous — 
I. acutifrons . 
f /. sordidus. 
Upper Jone to three) spines of the supra-anal series modified 
and enlarged — 
Upper spines like the others — 
J/. acutifrons. 
\l. agilis. 
{/. sordidus. 
(P. spinifer. 
