DESCRIPTIVE REMARKS. xh 
Ptilodictya lanceolata, fig. 4, is abundant; Fenestella subantiqua, fig. 5, 
and F. Millert, are common fossils at Dudley, &c., in the limestone. 
Bracurorop SuHetxs, though not so plentiful (either in number or spe- 
cies) as in Lower Silurian rocks, are still very abundant. Four species 
of Pentamerus and one of Stricklandinia (formerly included with 
Pentamerus) are recorded as Wenlock fossils; only two of these, P. 
linguifer and S. lirata, Pl. xv., fig. 4, continued from the Llandovery 
strata, the remainder being all distinct; P. galeatus, Pl. xx., fig. 5, as 
mentioned in the Explanation of the Plates, p. 59, is common to the 
Wenlock and Ludlow, continuing into the Devonian formation. The 
characteristic Brachiopods alluded to in the description of the fossils of 
the Wenlock shale (ante, p. xii), as ranging from the Lower to the 
Upper Silurian, such as Orthis elegantula, Pl. xx., fig. 7, which is 
equally abundant in both divisions, Strophomena depressa, fig. 9 (now 
referred by Mr. T. Davidson to S. rhomboidalis, “Brit. Sil. Brach.” 
p- 281), ranging from Caradoc to Ludlow, passing up into the Devonian, 
and continuing during the Carboniferous period (according to Mr. 
Davidson), the greatest range of any known shell; S. euglypha, fig. 8, 
ranging from Llandovery to Ludlow rocks, and Atrypa reticularis, 
fig. 4, are also very frequent in the limestone; the last-named species 
commencing in Lower Llandovery strata, ranges through all the Upper 
Silurians tothe Upper Devonian. Spirifera plicatella, fig. 1, S. elevata, 
fig. 2, and Meristella tumida, fig. 3, are also very common shells in the 
limestone, having a corresponding range from the Llandovery to the 
Ludlow rocks; Rhynchonella borealis, fig. 6, also recorded as a Llando- 
very species, is exceedingly plentiful in Wenlock limestone. Obolus 
Davidsoni, P\. xix., fig. 6 (before referred to, p. xli.), and Orbiculoidea 
Forbesti, fig. 7 (formerly Orbicula), are rarer limestone species. 
The Conchifera consist for the most part of shells allied to the 
recent Mytilus, Arca, Nucula, and Avicula; to the latter belongs Plerinea 
orbicularis, Pl. xxi., fig. 1, abundant in the Dingle District, Co. Kerry; 
the small shell doubtfully referred to the same genus, P. planulata, 
fig. 2, is frequent in the Wenlock rocks. The Mytiloid shells are also 
an important group: Modiolopsis antiqua, fig. 3, and MM. gradata, fig. 4, 
are common Wenlock fossils, the latter being also a Ludlow species. 
Grammysia cingulata, fig. 5, belongs to a genus of shells remarkable for 
the deep furrows on its valves; it has been found in South Wales, 
Westmoreland, and in Ireland; and Pleurorhynchus equicostatus, fig. 6, 
a Wenlock fossil, is a small species, belonging to a genus representative 
of the Cardiacea, which commenced existence in the Caradoc series of 
the Lower Silurian strata. 
Untvatve Saetts, Gasteropoda, occur throughout the Upper Silu- 
rians, and is not unfrequent in the Wenlock limestone; amongst the 
common forms are the spiral shells, Zuomphalus alatus, fig. 7, a Wen- 
lock and Ludlow species, abundant in the Dingle District of Ireland; 
E. rugosus, fig. 8 (with its probable variety, Z. discors), and E. funatus, 
fig. 9, which is the most common, and has the greatest vertical range ; 
its concentric operculum, fig. 9, 4, is often found fossil, and assists in 
