PYRAMIDULA. 



Genital system simple, lacking accessory organs. Penis receiving 

 the vas deferens and the retractor muscle at its summit. Spermatheca 

 bulbous, its duct very long. Ovi-sperm duct very much convoluted, 

 the ovo-testis consisting of small groups of large club-shaped follicles. 

 Eye-peduncle retracted between the branches of the genitalia (pi. 

 11, fig. 20, P. alternate* Say. PI. 11, fig. 27, P. strigosa Gld.) 



Jaw strong and opaque, arcuate, with a slight or obvious median 

 projection; surface rather faintly subvertically striated (pi. 11, fig. 

 18, P. alternata. PI. 11, fig. 17, P. strigosa). 



Kadula: Central teeth having the mesocone long, side cusps 

 small. Laterals having a large mesocone and a well developed 

 ectocone ; no entocone. Marginals similar, but with the basal plate 

 short, as usual (pi. 11, fig. 23, P. alternata). This type of dentition 

 is common to P. alternata, solitaria and idahoensis. In P. cumber- 

 landiana the side cusps are obsolete on central and inner lateral 

 teeth. 



In P. strigosa and haydeniihe central and lateral teeth lack ecto- 

 cones. The outer marginal teeth have an ectocone developed, and 

 sometimes it is split into two minute cusps (pi. 11, fig. 28, P, 

 strigosa). 



The Patulas of eastern America are oviparous, tire eggs small, 

 round, not hard-shelled. P. strigosa and its allies are viviparous, 

 four to six young occupying the uterus at the same time, the most 

 mature having a shell of 2j whorls, 3 to 4 mill, diameter, the earlier 

 2 whorls with fine oblique and spiral striae, marked off by a distinct 

 line from the latter third of a whorl, which is spirally lirate and 

 more or less hirsute. The viviparous mode of reproduction has 

 probably been assumed on account of the aridity of the Rocky 

 Mountain region. The rains are in this area uncertain, and for 

 snails mainly unseasonable ; and probably insufficient to insure the 

 development of eggs committed to the earth in the usual way. 



Snails of this section are distributed over the whole of the United 

 States except the Californian slope. Individuals of the species are 

 numerous, P. alternata in the East and strigosa in the West being 

 among the commonest of land snails. They live by preference in 

 rocky places, the talus of a limestone cliff being a favorite station. 



The species are polymorphic to a degree inconceivable to those 

 who have not actually seen large series of the shells. P. alternata 

 fergusoni and P. cumber landiana seem to be the extremes of one 

 series of forms, and P. idahoensis and haydeni of another. 

 4 



