DISCINID A. 63 
hitherto found are in an incomplete condition, and the absence of all knowledge 
with reference to its interior must leave us still uncertain whether it belongs to the same 
genus or sub-genus as O. plumbea. 
Position and Locality. Dr. Holl states, at p. 89 of his very interesting memoir on 
the Malvern Hills, that O. Phillipsii is found in the felspathic Hollybush sandstones of 
the Malvern Hills, representing the middle division of the Lingula-beds of North Wales. 
Famity—DISCINIDA. 
This family is composed of several genera and sub-genera ; but in our British Silurian 
rocks Discina (including Zrematis and Orbiculoidea) only have been hitherto discovered. 
In all the species the shell was attached to marine objects or rocks by a pedicle passing 
through an aperture or foramen in the ventral valve. 
Genus—Discina, Lamarck. 
Syn. Orbicula of Sowerby and of many other authors (not of Cuvier). 
Ref. Davidson’s ‘General Introduction,’ p. 126. The anatomical structure of 
Discina, as regards its muscular and other internal arrangements, has not been hitherto 
sufficiently examined. Zrematis does not seem to possess characters of sufficient import- 
ance to warrant its positive admission as a distinct genus. Our reasons for this are 
stated under Discina (Trematis) punctata. The internal characters of Orbcculoidea have 
not yet been discovered ; still, we retain the name provisionally as a sub-genus of Discina, 
with doubly convex valves. 
Discina RuGaTA, Sow. (sp.) Pl. V, figs. 9—18. 
OrBicuLA RUGATA, Sow., in Murchison’s Sil. System, pl. v, fig. 11, 1839. 
— — Dav. Bull. Soe. Géol. France, 2nd ser., vol. v, p. 334, 1848. 
DIscIna _ M‘Coy. British Paleozoic Fossils, p. 190, 1852. 
— — Salter. Siluria, 2nd ed., pl. xx, figs. 1, 2, 1859. 
Spec. Char. Nearly orbicular, sometimes a little longer than wide or longitudinally 
oval and slightly narrowed posteriorly. Upper or free valve of a low conical or limpet- 
like shape. Vertex situated at variable distances between one third and one fifth the 
