92 



before mentioned. We may incidentally mention here, that in his 

 description of G. incurva, he says it ought to be named G. rugosus, 

 as having been first figured under that denomination in the last century, 

 by Lang, in his Historia Lapidum, &c. T. 48, f. 1 and 2. He 

 attributes all such modifications of this form as Gr. obliqua, and Mac- 

 cullochii to this species; the most remarkable of these to difference 

 of age ; and consequently to the greater or less expansion of base, at the 

 time of the larger valve acquiring its freedom : in illustration of this he 

 gives a figui'e, T. 9, f. 9, (which is an exaggeration of our own Figure 6, 

 Plate 2,) with the following observations : — " As such causes produce similar 

 results in all the Jurassic Gryphites, I do not think these last should be 

 considered oysters, although they bring to mind O. irregularis, before 

 mentioned. (Page 48, Jura.) What is most remarkable is only this, 

 that the axes of upper valves, not truncated, but, exogyrseform, are 

 turned outwards. How easy for such abnormalisms to become here- 

 ditary, and so, apparently to degenerate into another species." 



Oppel, in his " Mittlere Lias Schwabens," imder his Ostrea Amalthei, 

 makes the following remarks, on separating these shells into distinct 

 species : — " Goldfuss figures, an O. irregularis, from the lias marl, of 

 Linz, and we have similar examples in our lower NumismaHs-marl, 

 with G. cymbium and G. obliqua. In Table 4 and 8 I have figured 

 such a one, to which is attached Ostrea cymbium; nevertheless, this 

 oyster passes completely into Gryphaea, when its point of attachment 

 becomes somewhat smaller, and changes with its growth from G. cymbium 

 to G. obliqua, and the latter to O. irregularis ; so that when many 

 examples are placed together I am not able to define the distinct limits 

 between 0. irregularis and G. cymbium. As we have similar variations 

 of form between G. arcuata and G. calceola, so are O. irregularis, as 

 well as G. obliqua, to be considered as individuals of G. cymbium, 

 whose large, attached surface, has deranged the entire form of the 

 sheU." 



ZiETEN figures, as G. incurva var. lata, the G. obliquata of these 

 pages, stating that it is found with G. incurva in great numbers, parti- 

 cularly at Betzgemuth, near Boll, while Oppel treats it as a distinct 

 species, and makes it the leading shell of a particular zone, above the 

 A. oxynotiis bed, and immediately underlying the Lias Gamma of Quens- 

 tedt. With Oppel's observation, as applicable to oiu* own district, we 

 entirely disagree, as we find specimens of G. obliqua plentiftdly with G. 

 incurva wherever it occurs, (of which it can easily be proved to be 

 but the half grown stage,) exhibiting aU the eccentricities of which 

 that form is susceptible. 



The shell which he calls G. obliqua, and places doubtfully in his 



