664 FRANK COLLINS BAKER 
PHYSIDAE 
Physa sayu Tappan ? 
A single immature shell is referred doubtfully to this species. 
It has the characteristic shape of a half-grown sayzz and is covered . 
with heavy impressed spiral lines. The individual has 44 whorls 
and is 12mm. long. Say is a common species in northern Illinois 
and the states to the north. 
Physa gyrina Say 
The shells of this protean species occur in abundance in the 
marl deposit; the greater number of individuals, however, are 
immature, only about 3 per cent being fully mature. The largest 
specimen has 6 whorls and measures 26mm. in length. Gyrina 
is distributed quite generally over the state and in the states north 
of Illinois. 
PLANORBIDAE 
Planorbis trivolvis Say ; 
Not common in the marl deposit and the majority of individuals 
are immature. Tvrivolvis is a very common species in Illinois and 
adjacent states. 
Planorbis parvus urbanensis Baker, n. var." 
This new form of Planorbis parvus occurred sparingly in the 
marl deposits and was apparently not as abundant in the post- 
glacial pond as the typical parvus usually is in ponds of a similar 
character. Typical parvus occurs living in the vicinity of Urbana. 
Planorbis altissimus Baker, n. sp.* 
This new species of Planorbis is represented by a few adult 
individuals and a number of young and immature specimens. It . 
was apparently not as common as the variety of parvus listed above. 
LYMNAEIDAE 
Galba refleca (Say) 
This Lymnaeid occurs plentifully in the marl deposit and is 
very abundant and variable; the majority of individuals, however, 
are young or immature. Reflexa is commonly distributed over the 
greater part of Lllinois. 
t The new Planorbes will be described in the current number of the Nawtilus. 
