Page:VCH Herefordshire 1.djvu/84

 A HISTORY OF HEREFORDSHIRE First on the list stand two spines obtained by Mr. J. E. Lee from the Lower Old Red Sandstone (passage-beds) of Tin Mill, Downton, near Ludlow, which is apparently in Herefordshire. These were described by Agassiz in 1837, and again in 1845, under the name of Ctenacanthus ornatus, but are provisionally assigned, with the same specific name, by Dr. A. Smith Woodward ^ to Climatius, a genus of primitive sharks belonging to the group Acanthodii, characterized among other features by the presence of dermal appendages to the gill-arches, which probably took the form during life of frills of skin. Similar spines are known from the Old Red Sandstone of Worcestershire. From both the Upper Ludlow beds and the Lower Old Red Sandstone (at Ledbury) of the county have been obtained spines of an unclassified shark- like fish which has been named Onchus murchisoni. It has been stated that some of the type specimens (now lost), which apparently came from Here- fordshire, were the remains of crustaceans, but others appear to have been fragments of fish-spines. Be this as it may, undoubted fish-spines from near Ludlow and Ledbury, in the collection of the British Museum, exhibit the distinctive characters recorded by Agassiz in his original description.* Other spines of the same general type from the Upper Ludlow and the Downton Sandstone at Kington and the Lower Old Red Sandstone of Ledbury indicate a second species of the same genus, which should be known as 0. tenuirostris, although it has also received the name O. semistriatus. Yet other specimens from the county have been doubtfully assigned to the so-called genus Ptychacanthus^ typically from the Old Red Sandstone of Monmouthshire, More remarkable still are certain dermal tubercles, probably of Ostracodermi, from the Upper Ludlow bone-bed of the county, which have been made the type of the genus and species Thelodus parvidens. Similar tubercles have been found in the Ludlow bone-bed at Norton, near Onibury, Shropshire, and in the Isle of Oesel, in the Baltic ; * and complete examples of the fishes to which they belonged have deen discovered in the Upper Silurian of Lanarkshire, Scotland. Coming to the above-mentioned armoured Ostracodermi, we have in the section Heterostraci, which includes only the single family Pteraspididae, the typical genus Pteraspis represented by the two species P. rostrata and P. crouchi, both these having apparently been named on the evidence of English specimens. Remains of these species occur chiefly in the Lower Old Red Sandstone near Downton Hall, Whitbatch, and other spots in the neighbourhood of Ludlow. Pteraspis, as now understood, is characterized by the possession of a complex external dorsal shield, carrying a spine on the hinder edge, while the ventral shield is simple. Such ventral shields have been made the types of so-called genera and species under the names of Scaphaspis (or Cephalaspis) lloydt and S. lewisi? A remarkably fine specimen of one of these ventral shields from Kentchurch Hill, near Pontrilas, Here- fordshire, was presented to the British Museum in 1889 by Mr. J. F. Symonds. A second genus of the same family, Cyathaspis, was founded on specimens from the Upper Ludlow beds and Downton Sandstone of the county. This ' Cat. Toss. Fish. Brit. Mus. ii, 32. 'Ibid. 94. ' Woodward and Sherborn, Cat. Brit. Toss. Vertebrates, 169. ^ Woodward, op. cit. 158. ' Ibid. 1 64.-5. 36