POLYGYRA. 75 



(the portion everted during copulation) is smooth inside (fig. 15) ; 

 it extends upward in a sort of sheath over the base of the upper 

 portion (figs. 12, 15). This sheath is what Leidy and Biuney call 

 the " prepuce." The upper portion has fleshy walls which are 

 densely corrugated or subgranulated within, and the cavity is almost 

 filled by a thick longitudinal corrugated column,adnate throughout 

 its length to one side (fig. 15, penis slit open longitudinally ; fig. 13, 

 14, transverse sections of penis with fleshy column). At the apex of 

 the cavity there is a perforated papilla (pi. 21, fig. 13, transverse 

 section), free at its lower end. The retractor muscle is inserted on 

 the vas deferens a short distance above the apex of penis ; its distal 

 end being attached to the floor of the lung cavity. The lower 

 part of the spermatheca duct (pi. 21, fig. 15) is swollen, with fleshy 

 walls which inside are strongly corrugated lengthwise (pi. 21, fig. 

 16, transverse section). 



Distribution : Eastern North America from Canada to Florida, 

 west to central Texas and Dakota; in the northwest occurring in 

 Idaho, and on the Pacific slope from Sitka to Santa Cruz, California. 

 Most of the species live around decaying logs or under and upon 

 decaying leaves in forests. Some, like multilineata occur in great 

 numbers on the low, weedy, willow covered flood-plains of rivers; 

 others, like profunda, prefer shady, leaf-carpeted and rocky hill- 

 sides. P. dentifera and P. palliata are found under the loosened 

 bark of hemlock boles, sharing these retreats with Philomycus. 

 Most species come from their hiding-places in the warm days of 

 early spring, and during rainy weather in summer. They may 

 then be found crawling upon the dead leaves, or ascending nettles, 

 etc., the leaves of which they eat. In sunny days after rain, they 

 are found adhering to the lower surfaces of nettle leaves. They 

 never ascend trees. 



The species enumerated below have been divided by authors into 

 two sections, Triodopsis and Mesodon ; but such division seems to be 

 artificial. Some species of Triodopsis. &YZ known to have varieties 

 lacking lip-teeth, and these would technically fall into Mesodon. 

 In other cases, such as the group of Ida.no and Washington species, 

 all the transitions from tridentate to toothless apertures occur. The 

 group of P. appressa is also a transition group. Tryon has resusi- 

 tated the section-names Xolotrema and Ulostoma. The first of these 

 is a Rafinesquian name totally unidentifiable ; the second was pro- 

 posed by Albers for species of Polygyra s. s. and Triodopsis s. s., and 



