40 MOLLUSCA FROM THE GREAT OOLITE. 



Mr. Sowerby remarks, " the small and nearly flat posterior lobe leaves the beaked end 

 of this Modiola so small as to give it much of the contour of a Mytilus, the depth of 

 the two valves together is greater than the width, and the length is twice the depth. 

 The roughness of the striae proceeds from minute elevated scales, that are most conspicuous 

 near the margin of the shell, and are nearly obliterated towards the beaks." 



It occurs somewhat rarely in the shelly beds of the Great Oolite, and likewise in the 

 marl bed of the Inferior Oolite in the Cotswolds. 



Localities. Forest Marble of Wiltshire ; upper marly beds of Great Oolite, at 

 Felmersham, Bedfordshire; Blisworth, Northamptonshire, &c.; Minchinhampton Common, 

 in the Great Oolite ; near Nailsworth and Cheltenham in the Inferior Oolite. 



MYTILUS LONSDALEI. Tab. IV, fig. 3. 



Testa ovato-oblongd, Icevigatd; antice latd, subdepressd, postice convexiore, angulo 

 obliquo formante ; umbonibusgracilibmincurvis, margine cardinali obliquo, curvato, margine 

 inferiore subsinuato ; laminis incrementi conformibm tenuibus, 



Shell ovately oblong, smooth ; anteriorly wide and depressed, posteriorly more convex, 

 divided from the anterior portion by an oblique and obtuse angle, which passes from the 

 umbo to the infero-posterior extremity; umbones slender, incurved; hinge border oblique 

 and curved, inferior border slightly sinuated ; the surface has numerous delicate irregular 

 laminae of growth. 



The general figure has some resemblance to Modiola sub&quiplicatd, Roemer, Verst., 

 tab. v, fig. 7, but the latter shell has greater convexity, the umbones are less attenuated 

 and the oblique angle formed by the anterior depressed surface is less distinct. It has 

 also some resemblance to M. imbricata, Sow., but is distinguished by the posterior 

 portion being less expanded and the general form more elongated. 



Length, 16 lines; height, 7 lines; diameter, through both the valves, 6 lines. 



Localities. Sapperton railway tunnel, in the Great Oolite. In the Cornbrash of Wilt- 

 shire it is abundant. 



MYTILCS COMPRESSTJS, Goldf. Tab. IV, fig. 7. 



MYTILUS COMPRESSUS, Goldfuss. Petref., t. 131, f. 11. 

 MODIOLA COMPKESSA, Portlock. Geol. Report, p. 122. 



Testa ovatd subconvescd, concentrice striatd; umbonibus subanticis, compressis, margine 

 cardinali recto, latere inferiore convexo-plano, postice subcompresso prorsum rotundato. 



Shell ovate, rather convex, concentrically striated ; the umbones subterminal and com- 

 pressed, hinge margin straight; inferior side moderately convex, posterior side rather 

 compressed and rounded. 



The anterior extremity is narrow and somewhat compressed, the posterior much 



