1 8 CONK LIN. [Vol. X 1 1 1 . 



anchored in the " codfish pool," a place where there was a large 

 supply of fresh and pure sea-water, and yet where the surface 

 was generally calm. In this box some of the veligers lived for 

 almost two weeks, but although there were stones and shells 

 in the box, I could not find any spat upon them at the end of 

 that time. From these facts it seems probable that the free- 

 swimming life of the veligers lasts not less than two weeks nor 

 more than three. The whole course of development, therefore, 

 from the time the eggs are laid to the close of the larval life 

 and the assumption of adult characters and habits, is from six 

 to eight weeks. 



The fertilized eggs in all four species are laid in capsules, 

 which are formed by secretions from the wall of the uterus or 

 nidimental organ.^ These capsules are united into a bunch, 

 like a cluster of grapes, by a common stem, which is fastened 

 to the shell, stone, or other object upon which the Crepidula 

 lives. This bunch is attached between the two folds of the 

 propodium, and within the mantle cavity of the mother, and 

 since the adults do not move about, it follows that the eggs 

 are always covered by the parent's shell. As a result of this 

 protection the walls of the egg capsules are thin and delicate ; 

 very unlike the tough, leathery capsules of most marine proso- 

 branchs. Within the capsules is an albuminous fluid, in which 

 the eggs are immersed, and which is absorbed by the embryos 

 in the course of development. Salensky ('72) has described 

 similar capsules and egg-laying habits in Calyptraea, a seden- 

 tary prosobranch nearly related to Crepidula. 



The approximate number of capsules and eggs deposited by 

 the mature females of the different species is shown in the 

 following table : 



1 The capsules in Urosalpinx cinerea are marked on the outside by faint spiral 

 lines, and show a tendency to tear in a spiral direction. The same is true of the 

 capsules of Crepidula, though in a less marked degree than in Urosalpinx. This 

 spiral structure is caused, I think, by the rotation of the capsule as it passes 

 through the uterus, in the same way that the spiral character of the egg mem- 

 branes of birds and reptiles is produced. 



