PECTEN. 149 
specimens which [ have seen, the concentric ornament on the right valve is indis- 
tinct, owing to the imperfect preservation of the surface of the shell, but in several 
cases the fine concentric grooves are clearly shown on the left valve. 
Pecten Darius, V@Orbigny,' from the Albian, is a closely allied form, but at 
present is known only by the brief description in the * Prodrome.’ The form from 
the Gault of Cosne, described by De Loriol® as P. Darius, appears to differ from 
P, orbicularis in the inequality of its ears; the figures do not show the character 
of the ornamentation satisfactorily.  Amusium suleatellum, Stoliezka,” and P. 
concentrice-sulcatus, Miller,! appear to be closely allied to P. orbicularis. 
The Senonian specimens described by Goldfuss, Holzapfel, ete., as P. laminosus, 
Goldfuss, and by Favre and Bohm as P. sublaminosus, seem to agree with those 
forms of P. orbicularis which have more numerous ribs than usual, and particularly 
with some examples from the Warminster Greensand and the Chloritic Marl of Maiden 
Bradley. Professor Holzapfel has kindly sent me eight specimens from the Aachen 
Greensand, but it is difficult to compare them satisfactorily with English examples 
owing to their different mode of preservation. There does not, however, appear to 
be sufficient reason to regard them as distinct from the Cenomanian forms of 
P.orbicularis. The ears in the example figured by Goldfuss are larger than is usual 
in P. orbieularis. 
P. membranaceus, Nilsson,’ is similar in form to P. orbicularis, but has the con- 
centric ornamentation very fine, so that the shell appears to be almost smooth. 
P, Nilssoni, Goldfuss,’ is also distinguished by being nearly smooth, and (judging 
from Goldfuss’ fig. 8/) is still further separated from this group by its deep byssal 
sinus. 
P. nummularis,’ Fischer de Waldheim,’ is a closely allied form, but without 
seeing a series of specimens I am unable to make a comparison. 
P. (Amusium) balticus, Dames,° is probably identical with P. orbicularis. 
1 «Pyodr. de Pal.,’ vol. ii (1850), p. 139. 
* « Faune du Gault de Cosne,” ‘Mém. Soc. Pal. Suisse,’ vol. ix, 1882, p. 84, pl. x, fig. 6. 
3 «Paleont. Indica, Cret. Fauna 8. India,’ vol. iii (1871), p. 136, pl. xxxi, figs. 12, 17. 
(ar 
> * Petrif. Suec.’ (1827), p. 23, pl. ix, fig. 16 (lower figure). See also Hennig, Holzapfel, Zittel, 
Geinitz, Goldfuss, ete. 
5 *Petref. Germ.,’ vol. ii (1836), p. 76, pl. xcix, fig. 8. 
7 Fischer de Waldheim, ‘Bull. Soc. Imp. Nat. de Moscou,’ vol. xvi (1843), p. 135, pl. v, fig. 4; 
WVOrbigny, in Murchison, de Verneuil, and Keyserling, ‘ Géol. de la Russie,’ vol. ii (1845), p. 475, 
pl. xli, figs. 20—23, and figs. 16—19 (P. demissus) ; d’Orbigny, ‘ Prodr. de Pal.,’ vol. i (1849), p. 373; 
Trautschold, ‘ Bull. Soc. Imp. Nat. de Moscou,’ vol. xxxviii (1865), p. 23, pl. iii, fig. 2; Nikitin, “ Les 
Vestiges de la Période Crét. dans la Russ. Centrale,’ ‘Mem. Com. Géol.,’ vol. vy, 1888, p. 73; 
P. demissus, Trautschold, * Bull. Soc. Imp. Nat. de Moscou,’ vol. xxxiv (1861), p. 268, pl. vii, fig. 4. 
8 *Zeitschr. d. deutsch, geol. Gesellsch.,’ vol. xxvi (1874), p. 762, pl. xxi, fig. 1.  Notling, 
5 
* *Mollusk. Untersenon von Braunschweig u. Ilsede’ (1898), p. 34, pl. v, fi 
‘* Baltischen Cenoman.,” * Palaeont. Abhandl.,’ vol. ii, p. 17, pl. ui, fig. 7. 
