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 costas, 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. 



PERN A MYTILOJDES, Lam. Tab. XXXII, fig. 3. 



PEKNA MYTILOIDES, Lanark. An. sans Vert., 6 Bd., p. 142. 

 Zieten. Pet., p. 71, pi. 54, fig. 2. 

 Gold/. Pet., p. 104, t 107, fig. 12. 

 D'-Orb. Prodrome de Pajeont., 1, p. 31 1, No. 21 1. 

 Morris. Catal., 1854, p. 1/9. 

 Oppel. Jura formation, p. 607, No. 79. 



Quenstedt. Der Jura, p. 383, tab. 52, fig. 8. 

 Damon. Geol. Weymouth, Suppl., pi. 2, fig. 5. 



Testa ovala-sigmoidea, convexo-plana in aJam brcvem producta, umbonibus acuiis 

 prominentibm, 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 OBLIQUA, Walton MSS. Tab. XXXIV, fig. 22 a. 



subaquivalvi convexo-plana, crassa, umbonibus acutis, prominentibus, maryui<> 

 antcriorc redo, mnryine cardinali recto, oblique dcclivi, vahis lamellis irregularibm 



