LINGULID A. 59 
space, which is not prolonged further than the anterior margin of the impressions, 
Surface smooth, marked with concentric lines of growth; shell-structure calcareo-corneous. 
Length 14, width 16, depth 5 lines. 
Obs. Prior to 1853 internal casts of this curious fossil had been found very abun- 
dantly in the Wenlock shales near Dudley and Walsall, as well as in those of other 
localities, but paleontologists were at a loss to determine the genus to which they 
belonged, and my friend Mr. Salter asked me to describe them for him. Having received 
about that period an extensive series of Russian examples of Odolus Apollinis and O. 
sculptus, I recognised that our English casts were referable to the Russian genus, and that 
they were the largest representatives of Odo/us known up to that period.’ 
Mr. Salter is of opinion that the specimens found near Walsall and elsewhere really 
belong to two or three distinct species ; but as Dr. S$. P. Woodward and myself felt at the 
time very uncertain whether sufficiently distinctive characters could be found to separate 
them .specifically, I preferred describing them provisionally as named varieties of O. 
Davidsoni ; and, indeed, there seems to exist every passage in shape between the typical 
form of O. Davidsoni and O. transversus. In Pl. 1V. I have figured many specimens, to 
show how much their interior markings vary in detail. 
Position and Locality. Wenlock shales, Rushall Canal, near Walsall, Dudley, and the 
Wenlock limestone of Benthall Edge; it has also been found in the Wenlock shales of the 
Malvern and Ledbury Tunnel (Mus. P. Geol.). In Ireland it occurs in Upper Silurian 
shales at Ferriter’s Cove; and imperfect specimens from that locality may be seen in 
the Museum of the Geological Survey, Dublin. It has also been obtained by Prof. 
Lindstrém in the Upper Silurian limestone of Gothland and Faro. 
Var. TRANSvERSUS, Salter. Pl. V, figs. 1—6. 
OBOLUS TRANSVERSUS, Salter, MS. Davidson’s Monogr., vol. i, General Introduction, 
p. 136, fig. 53, 1853. 
Shell transversely oval, depressed. Length 19, width 28 lines. 
Obs. In some specimens of Obolus Davidsoni the posterior margin is very obtuse and 
almost straight; the surface smooth and marked with concentric lines of growth; and 
on a cast found by Mr. Mushen, and figured in our plate there exist a number of spine- 
like impressions, which would lead us to suppose that the surface had been originally 
covered with spines. 
Position and Locality. This variety occurs in the same localities as the preceding, but 
is most abundant in the Wenlock shale of Parkes’ Hall, near Dudley, at Walsall, and also 
in the Woolhope limestone of Malvern. (Mus. Prac. Geol., and many cabinets.) 
' Some years later Mr. Billings discovered in Canada a very interesting large species of the same genus, 
to which he applied the specific denomination of O. Canadensis (‘ Geol. Survey of Canada,’ 1857). 
