592 PROCEEDINGS OP THE ACADEMY OP 



the adult presents a curious scalariform appearance under these circum- 

 stances. 



This species feeds on animal and vegetable food ; over one hundred were 

 taken from a decomposing salt cod-fish that had been thrown into the Erie 

 Canal. They have also been found feeding on Uniones recently dead. They 

 are most abundant in locations where refuse food from boats or other sources 

 accumulate in the Canal. 



The ovaries are usually free from young only a few weeks in early summer. 

 The number produced by an adult seldom exceeds thirty, and is often less. 

 Specimens have been found 1 9- 10th inches long. The usual dimensions of the 

 adult seldom exceed 1 6-10th inches. The proportions of the sexes are some- 

 what different in this species from those of decisa and rufa, there being a 

 somewhat greater percentage of males for this species. The females are about 

 eight times more numerous than the males. 

 Paludina decisa ? Say. 

 Paludina decisa, De Kay. 



This seems to be somewhat a stumbling block to naturalists in this country, 

 and writers who have endeavored to elucidate Mr. Say's writings on this 

 species, evidently imitate him in confounding two distinct species. Mr. Say's 

 figure of decisa in his American Conchology belongs to a group which embra- 

 ces P. ponderosa, Say, as its type, which species any one acquainted with the 

 soft parts would say is more nearly related to integra than to that species 

 which, by common consent among naturalists in the eastern portion of the 

 United States, (and evidently following Mr. Say's earliest types,) is called 

 decisa. 



The writer of this paper at one time confounded integra and decisa, and 

 continued in th; t ror until obvious and constant differences from the em- 

 bryonic young to the adult, forced the conclusion that they were distinct 

 species. 

 P. decisa. Soft parts. 



Spots less numerous than in integra, larger, brighter, circular, well-defined, 

 and separate, and not arranged radially as in integra. 



Mantle white, with scarcely any pigmentum nigrum. Embryonic young more 

 numerous than in integra ; no linear bands of pigment on the mantle. Length 

 ^ inch. Reversed specimens about two per cent, as in integra. No distorted 

 embryonic young yet observed. The reversed young seldom attain half the 

 size of the adult, and specimens have not yet been found with young. 

 No evidence has been presented that this species partakes of animal food. 

 Adults of this species sometimes attain a length of 1 J inches usually less. 



Paludina rufa, Haldeman. Soft parts. 



Upper surface of foot of a dark slate color, almost purple when seen in a 

 favorable light, marked with numerous small disconnected greyish orange 

 spots occupying less of the surface than in decisa. Tentacles dark, with a 

 pale margin. Mantle covered with pigmentum nigrum. 



Embryonic young nearly as large as those of decisa, the shell of a decided 

 pink tinge, translucent and with a polished epidermis. This last feature 

 characterizes the shell at all stages of development. Faint markings appear 

 on the mantle through the shell. 



The largest adults observed were nearly 1^ inches long. In these the last 

 whorl presents a flattened surface parallel with the surface of the preceding 

 whorls, with a somewhat well characterized angle between that surface and 

 the base of the shell. The angularity observable below the suture of integra 

 is never seen in this species, and the angularity on the middle of the whorl in 

 this species, is not seen in integra ; decisa has no angularities. 



Specimens of this species with well-marked bands have been observed. 

 Similar features have also been observed in integra and decisa, but in these 



[Dee 



