LYMNIDA OF NORTH AMERICA. 245 
GENITALIA (pl. XI, fig. D): Male organs: Penis small, narrow, 
with rounded head, two-thirds as long as penis-sac, which is of large 
diameter ; retractor muscles of penis one mill. in length, very slender ; 
penis-sac retractor 1.25 mill. long and about twice as wide as the penis 
retractor ; these muscles have their insertion close together in the colu- 
mellar muscle ; protractor muscles four in number, two wide, powerful 
anterior muscles entering the penis-sac by several branches, and two 
narrow posterior protractors; vas deferens four mill. in length; pros- 
tate, elongate, ovate, flattened, rounded at both ends; the anterior end 
gradually narrows to meet the prostate duct, which is about one mill. 
in length. 
Female organs: Receptaculum seminis roundly pyriform, rather 
large, its duct 1.75 mill. in length; first accessory albuminiparous gland 
long-ovate, placed near the vaginal opening. 
The organs of parva are very uniform. In several specimens 
examined, only one showed any variation and in this one the penis 
retractor was attached to the penis-sac retractor a short distance from 
its insertion in the columella muscle. (Pl. XIV, fig. E, 2.) 
Three specimens gave the following measurements : 
Penis= Penis Penis- Rec. Prost. Was. 
Penis. sac. ret. sac.ret. sem. duct. def. Shell. 
1.00 1.50 1.00 1.25 165 1.00 4.00 8.10 Des Moines (1) 
1.00 1.50 1.00 1.25 GD 1.00 3.00 7.00 x (2) 
1.00 1.50 1.00 ALS ner gy 1.00 4.00 6.80 -, (3) 
The measurements show great uniformity. In one specimen (No. 
2) the prostate duct was longer and the vas deferens shorter than in 
the other specimens examined. (Dissections Nos. 23133 and 23132.) 
The genitalia of parva are almost identical with those of wmbilicata. 
RANGE (Figure 22): Connecticut west to Idaho; James Bay and 
Montana south to Maryland, Kentucky, Oklahoma, southern New 
Mexico and Arizona. 
Parva is a characteristic species of the Upper Mississippian region, 
from whence it has migrated into the Canadian, Hudsonian, Columbian 
(via the Missouri-Columbia drainages), Coloradoan and Rio Grandian 
regions. In the East it has penetrated into the Nova Scotian region. 
Farva occupies a large part of the Canadian, Transition and Upper 
Austral life zones. It is absent, apparently, from the Gulf and South 
Atlantic states. Its metropolis appears to be the Upper Mississippi 
Valley and the Great Lakes region. It has been universally confused 
with humilis and modicclla. When it is differentiated from these 
species it will doubtless be found to be widely distributed. 
GEOLOGICAL RANGE: Pleistocene. 
