ite 
THE NATURAL HISTORY SURVEY. 307 
Man’s Run (Shimek); Rock Island, Ill. (Pilsbry); Rock Run, 
Joliet, Ill. (Ferriss). 
Geological distribution: Unknown. 
Habitat: Found at all seasons of the year adhering to 
shells of Anodonta plana, sticks, leaves, etc. (Shimek.) Found 
at Rock Run on sticks and leaves. 
Remarks: This comparatively rare species is known by its 
very oblique shell; in some individuals the apex fairly over- 
hangs the margin. It has been found only at Rock Run, Joliet, 
but will probably be discovered at other localities by careful 
and patient search. The shell has some resemblance to the 
genus Gundlachia, and Mr. Pilsbry (Nautilus, 1V, 48) says of it: 
“Certain indications led me at the time of finding this shell” 
(speaking of a specimen found at Rock Island, Ill.), “to refer 
it to Gundlachia instead of Ancylus ; and it may be worth while 
to follow this clew further. If my supposition proves to be 
correct, Gundlachia will furnish the most extraordinary case of 
dimorphism known among American mollusks.’’* 
FAMILY PHYSID#. 
“Foot: Pointedbehind. Buccal plate (when present) with- 
out accessory laterals. Lateral teeth comb-like, alternating 
with simple cusps. Base of central tooth broad, bifid; cusp 
with several denticles.” ‘( Dall.) 
‘“‘Genttaha: On the leftside.” (Dall.) 
Genus PHYSA Draparnaud, 1801. — 
Shell: Thin, polished, sinistral; spire more or less acute; 
aperture oval, rounded in front; columella provided with a cal- 
lus which is spread over the last whorl; peristome acute. 
Animal: With a long foot, rounded before, pointed be- 
hind; mantle reflected over a portion of the shell and fringed 
with finger-like filaments; tentacles long, slender, pointed; 
eyes situated at their inner bases; genitalia on left side; jaw 
chevron-shaped or absent, finely striated, with acentral fibrous 
projection; radula as described for the family (Fig. 107). 
The Physz are the most difficult to study of the fresh 
water shells. So variable are their specific characters that no 
less than seventy species have been described, and the sub- 
ject is in such confusion that few students care to attempt their 
study or collection. 
Pil a also The Nautilus, Vol. IX, p. 63, 1895, for further notes on this subject by Mr. 
ilsbry. 
