236 On the Gryphaea of the Gryphite Grit in the Cotteswolds. 



us somewhat of the true oysters ; it has also a lateral lobe and 

 sulcus, but much less prominent than in the Cotteswold shell, the 

 general elongated form resembling G. cymbiwn. M. Buvignier 

 considers it to be distinct from G. cymbium, and has named it 

 G. Broliensis*. 



The conspicuous sulcation and lobe which serves prominently 

 to distinguish the Cotteswold shell, is a feature which in a more 

 modified form is present in nearly the whole of the species of 

 this subgenus, of which it constitutes one of the characteristic 

 attributes ; for although the species of Gryphaea are more easily 

 distinguished than those of the true oysters, there exists never- 

 theless a large amount of variation. The adherent species will 

 be found to exhibit greater variability than the others ; it may 

 consequently be inferred, that the variation of form is connected 

 with the position which was accidentally retained by the attached 

 shell. The Cotteswold Gryphsea, which exhibits a considerable 

 difference of aspect, was frequently attached to another of the 

 same species, the shells being clustered together in masses. 



In conformity with precedents in similar instances, I dedicate 

 our Cotteswold Gryphsea to the author who first figured it in 

 the f Geology of Cheltenham/ and whose labours have contri- 

 buted so much to enlarge our knowledge of the fauna of the 

 Oolite. 



Gryph.ea Buckmanni. 



Syn. Gryphcea cymbium, Murch. Geol. Chelt. 1834, p. 10. 



columba, Lonsdale, in Geol. Proceedings, 1835. 



cymbium, Morris, Catal. Brit. Foss. p. 109, 1843. 



cymbium, Geol. Chelt. 2nd edit. 1845, p. 75, 



pi. 7. fig. 3. 

 Sp. char. Shell transversely ovate, very convex, irregularly and 

 concentrically laminated ; beak acute, incurved, with a small 

 adherent area; larger valve extended laterally, inflated and 

 bilobed, having a wide and deep sulcation which extends from 

 the beak to the lower border ; upper valve concave ; margins of 

 the valves sinuated. 



The deep sulcation in the dorsal surface separates a posterior 

 lateral lobe, which in the mature form has a diameter equal to a 

 third part of the entire valve : in the young state the posterior 

 lobe is but slightly developed, and the valves at that part are 

 thin, but the groove is always conspicuous. 



The species which most nearly approach G. Buckmanni are 

 G. dilatata, Sow., and G. controversa, Roemer ; but these latter 

 are much larger species, they are less inflated, and have the 

 dorsal sulcation much more superficial. 



* G£ol. et Pateont. D£p. de la Meuse, Atlas, pi. 5. figs. 7, 8, 9. 



