shape of the nine spines above the anus is different. The head is con- 
vex, resembling J. sordidus most nearly, but the antennules are much 
longer and more slender than in any other known species. They are 
0.17 mm. long and about 0.016 mm. wide, while the longest seta is 
0.084 mm. long. The antenne are almost exactly as in J. sordidus. — 
The labrum has the usual shape, as have the jaws and other append- 
ages. The margins of the shell are ornamented with spines simply 
pectinate or barbed as in J. agilis. In I. sordidus these spines are 
variously branched, and in that form alone of the European species, 
according to Kurz, is there a failure to perfect the moult; in our spe- 
cies, which has simply pectinate sete, the oid coverings are all but 
uniformly retained. The spines of the Jower posterior margin are 
from 0.16 mm. to 0.20 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. 
Mhe:shellmoulhed periodically... scsav-ves.ncctaacaceseeshascssederassencedae wee x rite : 
The shell not moulted Dwi retained: 2) ss... cssacesceesaneienccanedeceeneesareccns { 7 anne 
Antennules not more than eight times as long as broad.............2ee000 I. agilis. 
I acutifrons. 
Antennules more than eight times as long as broad............ceeeceeeeeeee I. spinifer. 
I. sordidus. 
| I. sordidus. 
Claw of post-abdomen: pectinate ro... 0.0.02 ncccssceses eae en clevedslesvaliadsesretnes T. acutifrons. 
; I, agilis. 
Claw of post-abdomen not pectinate.........ccccerscsccscssenetascsccescosserees L. spinifer. 
ATSELONS GPINEMNHTONG Ol ClAWi.c sts ncactees.seces s+sesteoadeeuon Aeeee leases eas I. acutifrons. 
I. sordidus. 
Fine bristles or none in front Of Claw. .........0:sssessscesssocncesnsenniacecevess | I. agils. 
: I. spinifer. 
Amns-opening near Ghel@laws:.:.-.n-scsssecss-nccnuecedaes wee os-aceheeeast-aatieies I. acutifrons. 
I. sordidus. 
Anus about midway of the posterior border............... suadean easeeees sence I. agilis. 
I, spinifer. 
Marginal spines:of shell much branchedin ci. nsec ces csesenessncuncscrcwssess I. sordidus. 
I, agilis. 
Marginal spines nowhere much branched............... cae Seance cuetratee I. acutifrons. 
I, spinifer. 
Elongated anal spines on either side, four or five, very long.............. I. spinifer. 
I. agilis. 
Elongated anal spines MOTe NUMETOUS ..........0..0.ecerccvevere ccs ncscecses {2 acutifrons. 
I. sordidus. 
Upper (one to three) spines of the supra-anal series modified erent aculifrons. 
CMIAT OCH ie. eccece«cpekeapedesesscisns sconecses ce tleesccannae Mlcals taaeie aa tater taree «>. LL. agilis. 
I, sordidus. 
Upper’spines like the Others or. voc .cccc0.. veeccncns ctocncsonecseccavertscsesnviensese L. spinifer 
oe ee 
