220 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
riorly the ordinary branchial coil, here shaped like a thumb and fore- 
finger. The young is of a different shape and bears a long spine, 
The male is known from figures recently published by Birge (’91). 
GENUS ILYOCRYPTUS. 
Form compact, short; head short, triangular, with large fornices 
forming a roof over the head; the posterior margin of shell nearly as 
long as the inferior; lower angle a broad curve; antennules two-jointed, 
basal joint very short, second joint straight, rather long; sete termi- 
nal, but one seta near the base; the four-jointed ramus of the antenna 
with but three (terminal) set; six pairs of feet, last pair rudimentary; 
tail large, as in Lyncodaphnia, anus elevated; intestine straight, with- 
out ceca, but an expansion near the rectum sometimes simulates one; 
the margin of the shell is bordered with long spines, which may be 
branched or simply pectinate. There is often, perhaps generally, a 
failure to entirely remove the moulted shell; when this occurs the 
newly-formed shell from each moult remains under the older ones till 
the animal seems to be wearing six or more overcoats, and the spaces 
so formed become filled with alge and filth till the animal is no longer 
able toswim. P. E. Mueller and Kurz, who seem to have seen only 
I. sordidus, agree that Ilyocryptus cannot swim, but poles along in the 
mud on the bottom by means of antennz and abdomen; our J. spinifer, 
on the other hand, swims freely till loaded up with old clothes and 
filth. 
This genus is also closely allied with the Lynceide. 
* Tlyocryptus sordidus Lievin. 
PLATES LV, Fias. 6, 10, 11; LVI, Frias. 15-17. 
Acanthocercus sordidus—Lievin, Leydig. 
Body higher than long; head small, terminating anteriorly in 
almost a right angle; posterior part of the shell margins covered with 
branching, thorny spines; antennules cylindrical; antenne short; four- 
jointed rami with no lateral sete; post abdomen large, broad; terminal 
claws with two spines at the base; anus in the middle of the posterior 
margin, which is very heavily armed with spines; a hairy abdominal 
process is present, according to Kurz. 
There are no anterior ceca (my statement that P. E. Mueller de- 
scribed such czeca was an error; see Notes on Cladoreca of Minnesota, 
p. 246). Length 0.78 mm. The tabulated comparison beyond makes 
a full description unnecessary. Birge reports this species from Wis- 
consin and it has been encountered in Minnesota. 
