89 



is easily done by tracing, in well cleaned examples, those lines of 

 growth of which the edges converge at the point, where the profile 

 curve of the external portion of the true apex commences, and from 

 which the lines of the ligamental fossa recede, it will be clearly seen 

 that it must once have so closely resembled the young of an oyster, as 

 to render it difficult to distinguish the one from the other. Havmg now 

 arrived at the conclusion that the young Gryphite must, for a penod. 

 more or less uncertain, resemble an oyster, it becomes interesting to 

 ascertain how long such resemblance might endure, and to what extent 

 it could proceed. In figures 5 and 5% Plate 2, we represent the upper 

 surface and profile of a shell which is attached to a Gryphite by a base 

 so large, furnished with an upper valve so rugose and convex, with 

 ridges following, and corresponding with, the inequalities of the shell 

 upon which it grew, exhibiting very obscure and irregular concentric 

 lines of growth, and an appearance so completely that of an Oyster, and 

 different to that of a Gryphite, that no one, who had never seen similar 

 specimens, in a series of still further advanced stages, could admit 

 its relationship in any degree to the latter : notwithstandmg which, 

 proof most complete to the contrary can be produced, by figures 6, 

 es 6^ Plate 2, representing the profile, upper, and lower surfaces of 

 a Ihell of this description, which have become free at a more advanced 

 age; whilst figures 1 and P, Plate 3, show another, which, apparently 

 unable to acquire its liberty, is developed, while still attached, into an 

 indubitable Gryphite. 



If we carefully examine the detached shell we may learn from it 



not only a portion of its own history, but so much of that of its 



neighbours, as will enable us to account for many of the peculiarities of 



these abnormal individuals. A reference to figure 4, Plate 4, will show, 



upon a little reflection, that in a shell of typical form, growing in the 



ordinary manner, its inhabitant enlarged the habitable space, by adding 



foliations to the front and sides of its shell, depositing at the same 



time, in the space nearest to the beak, which had become inconveniently 



contracted for its accommodation, could not be enlarged, and from 



which the animal's instinct led it to retire, a corresponding amount of 



shelly matter, and bringing forwards the proportionately expanding 



ligament, into its ever widening furrow, after itself. This furrow or pit 



is seen in figure 4, Plate 4, above referred to, and the shell itself well 



shows why the incurved portion of the beak, must have continued to 



increase in thickness and weight during the life of its tenant, whdst 



the opposite extremity of the chamber became thinner and weaker. 



It is apparent that the animal could not, under any circumstances, 



extend the space required for its habitation in a backward direction, 



