LYMNZIDA OF NORTH AMERICA. 247 
Pupilla muscorum, Succinea grosvenort, Vallonia gracilicosta and Pla- 
norbis parvus. Numerous exposures disclose the recent geological 
history of the region to perfection. The South Platte first excavated 
a rather deep valley with steep bluffs along the northwest edge, then 
it refilled that valley with perfectly stratified deposits for the most part 
of fine material, with some local gravel beds. It is in a stratum of 
the fine material that these shells have been found.” 
Ecotocy: Parva is to be searched for in wet, marshy places, 
generally out of the water, on sticks, stones or muddy flats. The animal 
is more prone to leave the water than any other of the Lymnzas. 
ReMARKS: Parva may be known by its peculiar bulimoid appear- 
ance. It is more slender than humilis, has a longer, more turreted 
spire, a more regularly elliptical aperture and a differently shaped inner 
lip, which is roundly and broadly reflected over the umbilicus. Some 
specimens resemble in outline a miniature Campeloma as recorded by 
Lea in his description of curta. Occasionally specimens will be found 
in which the whorls are more or less shouldered, the umbilicus is more 
widely open and the sutures are more deeply impressed. (PI. XXIX, 
fig. 8.) The sculpture of the surface varies, in some examples the 
shell being smooth while in others there are very fine revolving lines. 
Parva also resembles wmbilicata, but may be known from that species 
by the shape of the inner lip, which stands erect in parva while it is 
jiattened out and excavated, especially at its junction with the parietal 
wall, in wmbilicata. The spire is longer and narrower, the sutures are 
more deeply impressed and the whorls rounder in parva. Parva is a 
common species and will probably prove to be widely distributed. ° 
When adult and perfectly formed it is one of the most graceful and 
kandsome of Lymnzas, with its rounded whorls, deep sutures and 
elliptical aperture. It varies somewhat in corpulency, some specimens 
being narrow while others are quite robust. The aperture varies from 
almost round to long-ovate. 
Parva resembles truncatula somewhat, but is easily distinguished 
by its more elliptical aperture and longer, more attenuated spire. The 
umbilical region and columella are also different. Though resembling 
iwmilis, it is quite distinct and was erroneously placed in the-synonym 
ci that species by Binney. It is probable that a number of the records 
of humilis were founded on parva, but as it is impossible to examine 
the original specimens upon which the records were made, their au- 
thenticity cannot be verified. 
The types of Lea’s parva are all small, immature specimens, His 
curta is large and robust, representing the adult form of parva. A 
