88 



by GoLDFUSs, as G. MaccuUochii ; but for ourselves, after carefully 

 comparing a great number of similar forms from other beds, and the 

 figures given by Goldfuss, Sowerby, and Terquem, we can discover 

 only such differences of degree, and not of kind, as have induced us to 

 consider all the forms hitherto presented to be mere varieties of 

 Gryphsea incurva. Sowerby's figure of the Shell upon which he 

 based his species of Gryphsea Obliquata, carresponds in general 

 character with our own figures 5, 5*, 5^, Plate 3, taken from speci- 

 mens of the same type ; but we must remark that his drawing is as 

 incorrect, as the specimen itself from which it was made must have 

 been imperfect, lines of the ligamental fossa being continued in 

 the engraving over the apex of the shell, from which the lines of 

 growth commence ! 



Figures 6, 6^ 6^, 7, 1\ 1^, Plate 3, Figures 1, 1*, l^, 2, 2% 2\ 

 Plate 4, represent forms intermediate to the last, to the various forms 

 called G. cymbium, by Goldfuss, and to G. MaccuUochii, of other 

 Authors, found in various beds ranging from that of Ammonites 

 Bucklandi, at Purton, to those exposed in the brickyard at Honey- 

 bourne Station ; these, and the specimens exhibited in conjunction 

 with them, agree perfectly with many published figures to which the 

 distinctive appellations quoted have been assigned; but with the 

 series at our disposal before us, it is impossible to separate them, even 

 as well marked varieties, from Gryphaea incurva. 



We will now take into consideration, the actual vertical range of 

 this species, which extends we believe nearly to the base of the 

 Liassic formation, and much lower than the beds in which it first 

 becomes known to us by the name, which we have hitherto applied to 

 its commonest form. This question we shall be better able to discuss 

 after the examination of other forms, which occur within the same or 

 neighbouring limits. 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 depended 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. Most of those 

 hitherto exhibited and figured, must have freed themselves compara- 

 tively early, as in none of them is the once attached surface, sufiiciently 

 large to break considerably the regular curve of its outline, whilst in 

 some of them, it is so obscure as to be traced with difficulty. 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 



