OP CONCHOLOGY. 135 



specimen was 59 ; reversed young 0. The largest number of re- 

 versed young was 2 in each of three specimens containing re- 

 spectively 20, 26 and 37 young each. Of seven other specimens, 

 selected on account of their size, the average number of young 

 was 49 to each adult ; the least number being 35, the greatest 

 being 64 and 67. The percentage of reversed young was about 

 5 per cent. 



The aggregates of all the specimens of obesa examined may 

 be briefly stated as follows : 31 specimens have each an average 

 of 28 young ; the reversed young being about 5 per cent. The 

 young are globose ; spire more depressed than in Integra. 



A second species observed among the shells sent by Mr. Moores 

 presents some deviations from the results found in the examina- 

 tion of obesa. A more slender shell than the preceding produces 

 a larger average of young ! The young do not differ much in 

 size and form, those of the latter species having the apex very 

 slightly more elevated. On account of the greater number of 

 young observed in this species, I shall for present convenience 

 call it fecunda, omitting to describe it as a species to be recog- 

 nized until more extended observation confirms my views re- 

 specting the specific tests to be derived from the embryonic 

 young. 



Of eight specimens offecunda containing young, the average 

 young for each adult is 43. The reversed young were less than 

 1 per cent., by a small fraction. 



Of the aggregates of all the specimens examined, the average 

 young to each adult is 34-4. The reversed young are only 2 per 

 cent., — being in marked contrast with the greater percentage of 

 reversed young in obesa. 



A third species, apparently identical in all its outward charac- 

 ters with shells of the Erie Canal, which, with deference to De 

 Kay, I have called Integra, presented on examination some pe- 

 culiarities that I have never observed in the Integra of the Erie 

 Canal. The Erie Canal shells, on being boiled, usually permit 

 the soft parts to be withdrawn without fracture or tearing. If 

 a portion of the soft parts remains in the apicial whorls, a fine jet 

 of water issuing with a force equal to 100 pounds to the square 

 inch, properly directed into the shell, at once removes the re- 

 maining soft parts. The Ohio Canal shells invariably retained 

 the soft parts within the apicial whorls, and no amount of force 

 applied to the injected stream of water could be made to remove 

 them, except in a few instances. Eight specimens contained 64 

 young, averaging 8 to each specimen. The gestatorial sack was 

 narrow, and the young were separated from each other by con- 



