ON THE STRATA OF LINCOLN. 553 



young had made its way within the half-closed valves of a 

 Lithodomus, it is difficult to imagine that this process could 

 go on in a second, third, or even fourth instance, since in each 

 case the death of the previous inhabitant must have been a 

 necessary condition ; and the former occupant, which could 

 have obtained entrance only in a very young state, must have 

 lived long enough to fill the entire cavity with its shell. It 

 is difficult also to account for the fact of the same species only 

 of Modiola enveloping each other, upon the supposition of a 

 fortuitous occupation of the empty shell by the young animal ; 

 since as there are more than one species of Modiola in the 

 same locality, it would have been quite as easy for one of 

 these to have made its way in as the other. 



A case somewhat analogous had recently come under my 

 observation through the kindness of a friend, in the instance 

 of the Saxicava rugosa, in the interior of which specimens of 

 Venerupis perforans are sometimes met with. But in this 

 case the size of the contained shell does not at all correspond 

 with that which contains it, and moreover the one Venerupis 

 does not in any instance contain another. 



[A series of specimens illustrative of the present communication have 

 been kindly submitted to our examination by Mr. Jelly ; and from these 

 we selected the two of which representations are given (fig. 69). We can 

 suggest no other explanation but the obvious one of supposing that the dead 

 shell of the Lithodomus was occupied by a Modiola, and the Modiola itself 

 subsequently occupied by a smaller individual of its own species ; the same 

 thing being repeated, in some instances, five or six times. The introduc- 

 tion however of the Modiola in the adult state would be opposed by the 

 physical condition in which the Lithodomus is placed. Any suggestions or 

 observations from our conchological readers, bearing upon this curious fact, 

 would be acceptable. — Ed.] 



Art. VII. — An Account of the Strata of Lincoln, from a recent 

 Survey, commencing North of the Cathedral, and descending to 

 the bed of the River. Drawn up by Mr. Wm. Bedford. 1 



The strata may be comprised in twenty-six beds, which 

 slightly vary and thin off, in some parts ; but lie horizontally, 

 from six to eighteen inches in thickness, (with the exception 

 of the Upper Oolite), till we descend to the Ochry Ferrugi- 

 nous-stone beds. 



1. Alluvial soil, from six to ten inches in thickness. 



2. Rubbly stone; — Cardia or stone cockles are profusely 



distributed here. 



1 Communicated by Sir Edward Ff. Bromhead, Bart. 

 Vol. III.— No. 35, n. s. 3 p 



