xlii DESCRIPTIVE REMARKS. 
only shells in this formation, as itis exhibited in Denbighshire and other 
parts of North Wales, occurring there in the greatest abundance ; Phrag- 
moceras of one or two species, and Lituites articulatus, Biddulphi, and 
occasionally L. giganteus (figured with the Ludlow fossils), Pl. 26, fig. 7, 
are conspicuous fossils in this stratum. 
The Trilobites, Znerinurus punctatus, Pl. xxiii, fig. 2,* E. variolaris, 
fig. 3; and Calymene Blumenbachit, fig.1, are characteristic. Cornulites 
serpularius (before cited), Pl. xix., fig. 2, and other Annelides, are some- 
times found, as well as stems and portions of Encrinites, complete 
fossils of this class being rare in this formation. Corals are in general 
similar to those of the Wenlock limestone, but fewer in number ; the cup 
corals, Cyathophyllum and Omphyma, Pl. xvu., fig. 4, with Favosztes 
alveolarisand F. fibrosus, Pl. x., fig. 1, ranging from the Llandeilo rocks 
to the Ludlow, being the most conspicuous ; the single form of Grapto- 
lite, G. priodon, Pl. xix., fig. 1, although commencing in Caradoc strata, 
is a most abundant and characteristic fossil of the Wenlock shale, con- 
tinuing on into the Ludlow rocks. 
Wentock Liuestone.—The profusion of Corals in this rock distin- 
guishes it from all the other Silurian strata, so that it resembles, in some 
districts, a coral reef. Some of the typical forms are figured on Pl. xvii. 
FHeliolites interstinctus, fig. 1; Havosites Gothlandicus, tig. 2; Halysites 
catenularius (the chain coral), fig.3; and Omphyma turbinata, fig.4; other 
common species are also mentioned in ‘‘ Siluria,”’ p. 120, viz., Cyatho- 
phyllum truncatum and C. articulatum, Favosites cristata and F. asper, 
Syringopora bifurcata, Alveolites Labechii, Acervularia luxurians, &c. 
This limestone is also rich in Crinoids, Periechocrinus moniliformis, Pl. 
xvil., fig. 4; an Encrinite with a bead-like stem, and occasionally 
five feet in length, is very abundant, covering large surfaces of the 
rock at Dudley, and occurring in detached fragments at other locali- 
ties; Cyathocrinus goniodactylus, fig. 1; Taxocrinus tuberculatus, fig. 2; 
Ichthyocrinus pyriformis, fig. 3; and Crotalocrinus rugosus, are com- 
mon Wenlock fossils. Cystideans, although rare, are characteristic; 
four genera only occur in the Wenlock rocks, including eight species, 
all distinct from those of the Lower Silurian. Examples of two of the 
most frequent species are figured on Pl. xviii, viz., Pseudocrinites 
quadrifasciatus, fig. 6, and Eehino-encrinus armatus, fig. 7. 
The Graptolites, so numerous and varied in form, in the slaty 
rocks of the Lower Silurian are reduced to but a few species in the upper 
division; for although in many districts the Wenlock shale and Lower 
Ludlow are crowded with them, it is only one species, Graptolithus 
privodon, before mentioned, Pl. xix., fig. 1, that is so abundant in this 
upper division. The AnnetipEs, Cornulites serpularius, fig. 2, and 
Tentaculites ornatus, fig. 3, are very frequent, especially in the limestone 
of Dudley, both having a considerable stratigraphical range. Potyzoa, 
although not so numerous in species in the upper as in the lower divi- 
sion, are not unfrequent in the Wenlock limestone; a large species, 
* The Tail of this Trilobite is also figured with the Llandovery fossils, Pl. 16, fig. 12, 
