150 
THE GEOLOGIST. 
the Gryjplma innirva of Sowerby, or arcuaia 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 : — Eourget, 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. arcuaia, Lamarck, 1801, Systeme des Animaux 
sans Yertebres, p. 398 ; G. arcuatay 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, Dic- 
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. 
arcuaia, Deshayes, 1831, Descriptions des Coquilles Caractcristiques des 
Terrains, p. 98, pi. 12, f. 4, 6 ; G. arcuaia, Goldfuss, 1835, Petrefacta 
Germanise, pi. 8, f. 1, 2 ; G. arcuata, Eoemer, 1836, Die Versteinerungen 
des ]N'ord-I)eutschen Oolithengebirges (Hanover), p. 62 ; G. arcuata, 
Schmidt, 1846, Petrefacten-Buch, p. 61, pi. 18, f. 3 ; Osirea arcuata, Des- 
hayes, 1849, Traite Elementaire de Conchyliologie, pi. 56, f. 8, 9 ; Osirea 
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 determinalDle ; 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. arcuaia. G. Maccullochii of Zieten, t. 49, f. 
3 ; G. Iceviuscula of Zieten, t. 49, f. 4 ; G. ovalis of Zieten, t. 49, f. 1 ; 
G. Maccullochii of Sowerby, t. 547, f. 1, 2, 3 ; G. gigantea of Sowerby, 
t. 391 ; G. obliquaia, Goldfuss, t. 85, f . 2 ; G. ohliquata 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, Eoemer ; O. irregularis, D'Orbigny, 1853, Prod. vi. p. 238 ; O. in- 
termedia, Ter quern; G.dej)7'essa,'Ph\\li'ps; G. lobaia,liu\\gmer. Although 
oysters have been found in much older formations, as exemplified by the 
unique specimen of Osirea nohilis, 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 
