112 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
Shell small, very oblique, convex; the anterior wing short, thick, and gibbose ; 
posterior wing more lengthened, emarginated posteriorly ; the middle of the valve with 
two elevated, oblique, longitudinal, distantly arranged coste, which are crossed by large 
irregular folds of growth; the right valve has not been obtained. 
Our sole specimen has the posterior extremity imperfect. 
Geological Position and Locality. 'The Great Oolite of Bussage, near Bisley 
Common ; collected by E. Witchell, Esq. 
Perna Mytitorpes, Zam. Tab. XXXII, fig. 3. 
Perna Myrtitorpes, Lamark. An. sans Vert., 6 Bd., p. 142. 
_— == Zieten. Pet., p. 71, pl. 54, fig. 2. 
— — Goldf. Pet., p. 104, t. 107, fig. 12. 
_ — D' Orb. Prodrome de Paléont., 1, p. 311, No. 211. 
_ — Morris. Catal., 1854, p. 179. 
— _ Oppel. Jura formation, p. 607, No. 79. 
— -— Quenstedt. Der Jura, p. 383, tab. 52, fig. 8. 
— — Damon. Geol. Weymouth, Suppl., pl. 2, fig. 5. 
Testa ovata-sigmoidea, convexo-plana in alam brevem producta, umbonibus acutis 
prominentibus, margine cardinali obliquo, foveolis (8-12) plano-concavis. 
Shell thick, ovately sigmoidal, with a moderate convexity, slightly produced pos- 
teriorly into a short imperfect wing; the hinge margin is wide, oblique with transverse 
pits from eight to twelve in number, and only slightly impressed ; the anterior border of 
the valves is much thickened and excavated. 
Geological Positions and Localities. The Forest Marble of Farleigh ; in the cabinet 
of W. Walton, Esq. Unfortunately none of the Forest Marble specimens are altogether 
perfect. The Geological range of this Perna must be very considerable, if there is no 
mistake in the identification of the species. Professor Quenstedt records it in the 
Inferior Oolite of Wurtemburg; Goldfuss, in the Oxford Clay and Upper Oolite of 
Baireuth and Wurtemburg; D’Orbigny quotes it from Villiers, Trouville, Lyon, 
Chaumont, Pizieux, Marolles (Sarthe), and other localities in the same department, 
all in his ‘ Etage Callovien.’ 
Mr. Damon has figured it from the Oxford Clay of Weymouth; and it has been 
recorded in the Kimmeridge Clay of the latter place ; and the Portland Oolite of Swindon, 
by Professor Morris. 
Perna oBiieva, Walton MSS. Tab. XXXIV, fig. 22 a. 
Testa subequivalvi convexo-plana, crassa, umbonibus acutis, prominentibus, margine 
anteriore recto, margine cardinali recto, oblique declivi, valvis lamellis irregularibus 
