Mollusks. 533 



believe is new to our Norfolk Fauna, was forwarded to me about the middle of Febru- 

 ary by a lady resident near Cromer, on this coast. This specimen, which was between 

 four and five inches in length, was caught in a sprat-net; and my correspondent in- 

 forms me that a larger specimen ("nine or ten inches long") had been taken on a line 

 a short time previously. Both specimens were taken off Cromer. — J. H. Gurney ; 

 Norwich, March, 1843. 



On the Development of the Purpura lapillus. By R. Q. Couch, 

 Esq., M.R.C.S.L. 



The Purpura lapillus is one of the most common shells to be found 

 on our shores ; but it is, however, more abundant in sheltered bays 

 and crevices of the rocks than in more exposed situations. It is ne- 

 ver, I believe, found in deep water, or in any situation where it can- 

 not be left dry during a short period in the recess of the tide. It is 

 therefore to be found between tide-marks, and that in great abundance. 

 It does not wander much from the spot in which it was formed ; the 

 greatest migration it seems ever to perform, is to some near crevice 

 where it can deposit its ova. The period in which they deposit their 

 egg- cases, extends from January to November ; but during the au- 

 tumn and winter they are by no means so abundantly to be found as 

 during summer ; and while deposition is going on, they assemble in 

 companies which fill the crevice. 



The ova are enclosed in elegant yellow vasiform capsules. They 

 are horny, and when recently deposited of a milky hue, which after- 

 wards becomes transparent. Superiorly they are hermetically sealed 

 by a large, solid, transparent plug; inferiorly each has a long and slen- 

 der foot-stalk, which spreads out into a thin incrustation as it comes 

 into contact with the rock, and by this means several become united. 



The crevices almost always selected for the deposit of their ova, 

 are those that are dry for several hours during the day ; and if they 

 are deposited in a pool, it is near the surface of the water. Those, 

 however, that have been placed in water take a longer time for deve- 

 lopment, and are more liable to abortion, than those which are alter- 

 nately submerged and exposed to the air. From this it would seem 

 that exposure to the air has a beneficial influence over their develop- 

 ment. And from what I have observed, it seems that the deposition 

 is chiefly effected during the recess of the tide, or at all events they 

 are abundantly deposited at those times, and apparently more than at 

 any other. 



It has been supposed that the cases have been first deposited and 



