Chap. X.] 
UPPEK SILUKIAN BIVALVES. 
229 
species, which is common at Dudley, is identical with one from the Upper Silu- 
rian of Bohemia. 
Next in importance are the Mytiloid Shells, represented by the genus Modio- 
lopsis * which contains several species. Thus M. complanata, PL XXIII. f. 1, 
is an Upper Ludlow fossil ; M. Nilssoni, Foss. 61. f. 8, is both a Wenlock and 
Ludlow species; and M. platyphyllus, f. 7, is characteristic of the uppermost 
Ludlow beds, where it occurs with some other forms, now referred by Professor 
M'Coy to his new genus Anodontopsis. To this group, which contains the more 
circular forms of the genus, belong Anodontopsis (M.) quadratus and A. ovalis, 
Salter, A. angustifrons, M'Coy, A. lsevis, Sow., and A. bulla, M'Coy, Foss. 61. 
f. 5. They are all species of the Ludlow rock. Mytilus exasperatus, Phill., and 
Modiolopsis antiqua, PI. XXIII. f. 14, are Wenlock fossils, the latter being 
common. Mytilus mytilimeris, Foss. 61. f. 6, is also plentiful in the Wenlock 
rocks. Goniophora cymbaeformis, PL XXIII. f. 2, seems nearly allied to Mytilus, 
and is one of the most abundant Upper Ludlow shells. Certain forms, less evi- 
dently related to this family, have been termed Orthonota by some authors, and 
Sanguinolites by others. They are thin shells, without hinge-teeth, and outwardly 
much resemble Mya, Panopaea, &c, to which, however, they are not in reality 
at all allied. Orthonota semisulcata (Modiola, Sil. Syst.), is one example from 
the Ludlow rocks, not figured in this work ; and 0. prora (Foss. 61. f. 4), is one 
of the most frequent fossils in the Tilestones of Westmoreland. Other species 
referred to this genus in the publications of the Geological Survey f differ still 
Fossils (61). Upper Silurian Lamellibranchtata.. 
1. Grammysia cingulata, Hisinger. 2. G. 
triangulata, Salter. 3. Orthonota angu- 
lifera, M'Coy. 4. O. prora, Salter (O. se- 
misulcata, M'Coy). 5. Anodontopsis bulla, 
M'Coy. 6. Mytilus mytilimeris, Conrad. 
7. Modiolopsis platyphyllus, Salter. 8. M. 
Mlssoni, Hisinger, 
more widely in outward appearance from Modiola, to which they are neverthe- 
less believed to be related. They are abundant in the Ludlow rocks, especially 
O. amygdalina, PL XXIII. f. 6, and its variety retusa, f. 7. This species often 
covers the surfaces of the uppermost stratum of the Upper Ludlow rock, to 
the exclusion of all other fossils ; and with it, more rarely, occur 0. impressa, 
PL XXIII. f. 3, and 0. undata, f. 4. But Orthonota rotundata, f. 5, 0. solenoides, 
f. 9, and 0. rigida, f. 8, are more common in the Lower Ludlow. O. angulifera, 
Foss. 61. f. 3, is an ornamented species, rare in the Ludlow rocks of Westmore- 
land, and looking like the Goniomya V-scripta of the Oolite. 
Grammysia, de Verneuil, is a genus resembling the shells last mentioned, but 
* [There does not appear, however, to be any decided character to separate these shells from the 
Modiola; of our own day.— J. W. 8., 1859.] 
t Memoirs, vol. ii. pt. 1. p. 360. 
