FRESHWATER AND LAND SHELLS. 53 



Plate XV., fig. 48, represents a female, with the parts protruded, as 

 she lay at the bottom of a basin of water. The inferior portion of 

 both sides of the sacciform branchiae are visible, and bordered with 

 black. The fringe of the mantle bordering this portion is furnished 

 with brownish palpi, of one-eighth to three-eighths of an inch long, 

 the two longest being the anterior ones, and opposed to each other. 

 This part of the mantle is in frequent motion, as if in the action of 

 throwing the water on the oviducts. 



Plate XV., fig. 49, exhibits a very different apparatus for this part of 

 the mantle. In the place of the palpi, we have a gray, spotted, fleshy 

 ciliatc prolongation of the mantle, which terminates in two long flexi- 

 ble feelers, nearly an inch long. At the posterior end of this portion 

 there is a remarkable black spot on each side, surrounded by a white 

 ring, presenting an extraordinary resemblance to an eye. 



The difference between these two forms of the same portion of the 

 mantle of the radiatus is truly curious. It seems difficult to be- 

 lieve it possible that they should not differ specifically. In the charac- 

 ters of the shells, however, lean find no difference whatever, and no one 

 has, I believe, thought of dividing the radiatus of our rivers. Further 

 investigation may throw some light on this apparent deviation in na- 

 ture, and I trust the attention of the observant naturalist will be given 

 to it. Circumstances have prevented me from following up these exa- 

 minations, but it is my intention to resume them again. 



I had commenced with the examination for sexual character with a 

 good deal of ardour, and intended to have carried this through every 

 month of the year, so far as the seasons permitted. The circumstances 

 alluded to above, prevented the execution of this being as complete as I 

 desired, and I propose to give extracts from my notes, rather than at 

 present to draw conclusions. 



Oct. 12, 1834. — I opened a large numberof shells from the Schuylkill. 



Twenty-five U. complanatus. These were all found to be without 

 charged oviducts ! ! 



Eleven U. nasutus. Four were found to be females, seven males. 



Twenty-four U. cariosus. Ten were found to be females, fourteen 

 males. 



VI. — o 



