150 



THE GEOLOGIST. 



the Gryphaa incurva of Sowerby, or arcuata of foreign writers, the lat- 

 ter being the name under which it was described by Lamarck, the typical 

 form of which has been figured by the following, amongst many other 

 authors: — Bourget, 1742, Traite des Petrifactions (Paris), pi. 15, f. 92 ; 

 Walcot, 1779, Description of Petrefactions near Bath, p. 51, f. 34; Ency- 

 clopedic, 1789, p. 189 ; G. arcuata, Lamarck, 1801, Systeme des Animaux 

 sans Vertebres, p. 398 ; G. arcuata, Parkinson, 1811, Organic Remains, 

 vol. iii. p. 209, pi. 59, f . 4 ; G. incurva, Sowerby, 1815, Mineral Concho- 

 logy, vol. ii. p. 23. pi. 112, f. 1, 2 ; G. arcuata, Lamarck, 1819, Animaux 

 sans Vertebres, vol. vi. p. 198, no. 4; G. incurva, Defrance, 1829, Die- 

 tionnaire des Sciences Naturelles, xix. p. 536 ; G. arcuata, De Blainville, 

 1825, Manuel de Malacologie et de Conchyliologie, p. 59, f . 4 ; G. incurva, 

 Zieten, 1830, Die Versteinerungen Wiirtemberges, p. 65, pi. 49, f . 1 : G. 

 arcuata, Deshayes, 1831, Descriptions des Coquilles Caracteristiques des 

 Terrains, p. 98, pi. 12, f. 4, 6 ; G. arcuata, Goldfuss, 1835, Petrefacta 

 Germanise, pi. 8, f. 1, 2 ; G. arcuata, Roemer, 1836, Die Versteinerungen 

 des Nord-Deutschen Oolithengebirges (Hanover), p. 62 ; G. arcuata, 

 Schmidt, 1846, Petrefacten-Buch, p. 61, pi. 18, f. 3 ; Ostrea arcuata, Des- 

 hayes, 1849, Traite Elementaire de Conchyliologie, pi. 56, f. 8, 9 ; Ostrea 

 arcuata, D'Orbigny, 1850, Prodrome de Paleontologie Stratigraphique, vol. 

 i. p. 220. It is, in fact, the shell invariably figured as the best type of the 

 subgenus to which it belongs, and cannot fail to be recognized from the 

 rudest figure, or from the following description, which is here somewhat 

 amplified from Sowerby. 



" Specific Character. — ' Elongated, very involuted, right side ' presenting 

 a more or less 'strongly marked, or an obscure lobe,' (when viewed with 

 the smaller valve placed downwards, and the umbonal portion turned away 

 from and at right angles to the front of the observer,) ' lesser valve ob- 

 long,' ' externally concave.' 



" This description applies only to the ordinary adult form, than which 

 none would appear at first sight to be more easily determinable ; but the 

 following list of what are considered by some authors of repute to be dis- 

 tinct species, and merely synonyms of one, by others, will at once give an 

 idea of the notable modifications and changes of form of which this spe- 

 cies is susceptible, the shells named in it representing every imaginable 

 gradation between the outlines of the common oyster and those of the 

 most perfectly developed G. arcuata. G. Maccullochii of Zieten, t. 49, f. 

 3 ; G. Iceviuscula of Zieten, t. 49, f. 4 ; G. oval/'s of Zieten, t. 49, f. 1 ; 

 G. Maccullochii of Sowerby, t. 547, f. 1, 2, 3 ; G. gigantea of Sowerby, 

 t. 391 ; G. obliquata, Goldfuss, t. 85, f . 2 ; G. obliquata of Sowerby, t. 

 112, f . 3 ; O. irregularis, Goldfuss, t. 79, f . 5 ; O. Iceviuscula, Goldfuss, t. 

 79, f . 5 ; O. ungula, Miinster, ' Handbuch,' (young,) t. 325 ; O. semicircu- 

 laris, Roemer ; O. irregularis, D'Orbigny, 1853, Prod. vi. p. 238 ; O. in- 

 termedia, Terquem; G. dejpressa, Phillips ; G. lobata, Buvignier. Although 

 oysters have been found in much older formations, as exemplified by the 

 unique specimen of Ostrea nobilis, from the carboniferous limestone of 

 Belgium, which may be seen in the British Museum, with others from the 

 Triassic ' Saliferian ' of St. Cassian, they amount in number of species, 

 in the opinion of Mr. S. P. Woodward, to three only, and it is first in 

 Jurassic strata that they make their appearance in any remarkable num- 

 ber or variety. 



" Taking into consideration this fact, with that of the universally admitted 

 variety of forms attributable to one species : to those who have interested 

 themselves in the theory of transmutation, as originally propounded by 

 Lamarck, subsequently by the author of the ' Vestiges,' and since, more 



