PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



151 



practically by Darwin, in his treatise ■ On the Origin of Species,' the ela- 

 boration of figures, and the minute details here presented, although ap- 

 parently uselessly repeated, may yet assume an aspect of interest which 

 they could not otherwise possess. Ostrea interstriata (Plicatida of Em- 

 merich) of the White Lias, and the small oyster which covers the slabs 

 of Lower Lias at Wainload, Westbury, Penarth, etc., associated with 

 Mudiola minima, recognized by Buckman and other local writers as Ostrea 

 liassica, are the earliest known to us in this district. Distinctly gry- 

 phoid forms occur considerably higher in the series, and are most abund- 

 ant from the zone of Ammonites BucTclandi, to that in which it is supposed 

 to be replaced by Gri/p/uca uhliqua; but any one who has carefully exa- 

 mined these in considerable numbers, and can therefore fully appreciate 

 the infinite diversity of form which they assume, rendering the determina- 

 tion of the differences between Oysters and Gryphites exceedingly per- 

 plexing, may possibly, in the sequel, feel disposed to adopt the suggestion 

 of Queustedt, that Ostrea liassica may really be the ancestral precursor 

 of the species under consideration." 



Six plates of illustrative specimens are given by Mr. Jones, and six 

 quarto pages of minute description and comparison. 



The actual vertical range of this species extends, Mr. Jones believes, nearly 

 to the base of the Lias formation, and much lower than the beds in which it 

 first becomes known to us by the name, hitherto applied to its commonest 

 form. " Upon close inspection, almost every specimen of Gryphsea will show 

 that it has been in its earliest stage attached, by the flattened or scarcely 

 rounded extremity of the beak, to a foreign body, and it is noticeable that 

 the symmetrical development of the adult appears to have mainly de- 

 pended upon the period at which it became free, the comparative duration 

 of which, in various individuals, being indicated by the extent of area so 

 rounded or flattened. . . . Upon transferring to paper the outlines of 

 that portion of the shell only which could have existed at the time of its 

 assuming its liberty, which is easily done by tracing, in well-cleaned ex- 

 amples, 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." Having arrived 

 at the conclusion that the young Gryphite must, for a period more or less 

 uncertain, resemble an oyster, Mr. Jones's figures specimens to show how 

 long such resemblance might endure, and to what extent it could proceed ; 

 one of these being attached by a base so large, the 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 con- 

 centric lines of growth, and an appearance so completely that of an oyster 4 

 and different to that of a Gryphite, "that no one," Mr. Jones says s "who 

 had never seen similar specimens, in a series of still further advanced 

 stages, could admit its relationship in any degree to the latter." 



Could the young animal, by its own volition, free itself from connection 

 with the body to which it had attached itself? This Mr. Jones thinks may 

 be answered allirmatively, from the fact, that in the majority of instances, 

 that connection could have endured but for a short time. The primary 

 point of adhesion must in general have been so small in the young fry, 

 and applied to surfaces so even, that a very slight exertion of force of any 

 kind, cither voluntary or involuntary, would have sullieed to detach it ; but 

 it can be readily conceived that in the event of adhesion taking place to 

 uneven surfaces, the union between the two bodies must have become so 



