LYMNZIDA OF NORTH AMERICA. 157 
is generally tightly closed, but in some specimens there is a small 
chink; sculpture usually strong. Nuclear whorls as in stagnalis ap- 
pressa. 
: Aperture 
Length. Width. length. Width. 
33.00 18.50 20.00 11.00 mill. Michipicoten Island. 
50.00 30.00 32.00 22.00 ~ higleyi. 
42.00 27.00 27.00 19100) - 
38.00 22.00 25.00 L200) a (type). 
49.50 29.50 32.00 50) © Siskowit Lake. 
45.50 27.00 31.50 100) = ss Se 
32.50 17.00 19.50 WOE). Sault St. Marie. 
34.50 18.50 21.00 ala ESTO) ee = a * 
34.00 20.00 22.00 T3LOO Ns es 
Sls (t 21.00 20.00 13008; Se NF 
Types: Sanctemarie, 2 specimens, No. 2682, Coll. Bryant 
Walker; jigleyi, 1 specimen, No. 23050, Coll. Chicago Academy of 
Sciences; cotypes, Coll. J. H. Ferriss. 
Type Locarity: Sanctemarie, Neebish Rapids, St. Mary’s 
River, Michigan; higleyi, Michipicoten Island, north shore Lake Su- 
perior. 
ANIMAL: Similar to stagnalis appressa. 
Jaw (Pl. VI. fig. B): Superior jaw higher than stagnalis ap- 
pressa, with a more acute central swelling; lateral jaws not differing 
from those of stagnalis appressa. 
RapuLa: Similar to that of stagnalis, but with eighteen laterals, 
the intermediate teeth beginning on the nineteenth tooth. 
GENITALIA: Similar in general to that of stagnalis appressa, but 
differing in details of the penis retractors. (PI. XIV, fig. B.) The 
penis retractor, instead of being inserted in the penis-sac retractor, 
as in appressa (pl. XIV. fig. A) is inserted in the columella muscle 
close to the insertion of the penis-sac retractor. In addition, there 
are two or three short muscles connecting the penis retractor with 
the penis-sac retractor. In one specimen the penis-sac retractor was 
split to form two muscles, the lower muscle being very heavy, with 
many insertions at its juncture with the penis-sac. (B, 2.) A speci- 
men from Sault Ste. Marie had the two retractors fused to form a 
broad band of tissue for about half their length to the insertion in 
the columella muscle. All of the muscles of the male system in 
sanctemarie are heavier than those of stagnalis appressa. 
Some characteristic measurements of the genitalia are given in the 
table below (dissection No. 23919) (Sault St. Marie) No. 23918 (Sis- 
kowit Bay) : 
