78 NEW- YORK FAUNA — MOLLUSCA. 



Physa PLICATA. 



PLATE V. FIG. 85. 



(STATE COLLECTION.) 



Description. Shell moderately solid, subovate, elongate, symmetrical. Whorls four to five, 

 rapidly attenuated to the apex. Surface with equidistant, longitudinal, and obsolete inequi- 

 distant transverse raised lines : suture distinct. Pillar-lip with a broad nacreous deposit. 

 Aperture rather more than two-thirds of the total length, acutely oval. 



Color. Amber, but coated with a black pigment : before this is removed, the aperture 

 is bluish iridescent. 



Length, 0-6-0-8; of aperture, 0-2-0-3. 



This description is from specimens of the largest size, obtained from a pond on New- York 

 island. It moves, like P. heterostropha, with great celerity on the surface of the water, with 

 its mouth downward. In some specimens the revolving and longitudinal lines are so distinct, 

 particularly the former, that the surface of the body-whorl appears covered with distinct square 

 facets. Some naturalists consider it only as a variety of heterostropha. It differs in many 

 important particulars from that species, but I regret that I have not been enabled yet to 

 examine the animal. 



Physa obesa. 



PLATE V. FIG. 86. 



(STATE COLLECTION.) 



Description. Shell ventricose ; when young, very thin and fragile. Whorls four to five, 

 rapidly attenuated to a minute and slightly elevated polished apex. Body-whorl inflated, with 

 its upper surface near the suture depressed, and forming an obtuse angle with the lower 

 portion : suture semicanaliculate. Surface polished, with minute incremental lines. Aperture 

 elliptical. 



Color. Pale horn. 



Length, 0'5; of aperture, 0'4. 



This species was communicated to me by Dr. Budd, who obtained it from the Mohawk 

 and Hoosic rivers, Rensselaer county. I have since received from the same gentleman, 

 specimens eight-tenths of an inch long, and quite solid, with a stout callus. Some naturalists 

 who have seen it, are disposed to consider it as identical with the following. 



