BIVALVIA. 141 



posterior extremity is destitute of costae ; the costae nearly of equal size upon both the sides 

 of the shell. 



The Lysianassa v-scripta of Goldfuss, Pet., t. cliv, fig. 6, is the Mya literata of 

 Sowerby, Phillips, and Agassiz. 



Geological position and localities. Great Oolite, Scarborough ; Kelloway Rock, Wilts ; 

 Cornbrash, Bedford ; Inferior Oolite, Brora ; Claydon, and the Cotteswolds. 



PHOLADOMYA OVALIS, Sow. Tab. XV, fig. 14. 



PHOLADOMYA OVALIS, Sow. Min. Con., t. '226. 

 ? PELAGTCA, Ag. Etud. Grit. Myes., p. 105, t. 2, f. 57. 



NANA, Phil. Geol. York., 1, t. 9, f. 7, (junior.) 



Testa elongato-ovatd, antice ventricosd brevi, postice elongate, anyusto, vix, hiante ; 

 umbonibus magnis, elevatis ; lateribus plicis longitudinalibm irregularibus et costis (circa 9) 

 distantibus angustis, subperpendicularibus. 



Shell ovately elongated ; anterior side ventricose, its margin closed ; posterior side 

 attenuated and elongated, its aperture small ; umbones large, elevated ; superior border 

 nearly horizontal, and sinuated, base curved elliptically ; the sides of the valves with 

 irregular longitudinal plications, crossed by costae, which are narrow, distant (about nine in 

 number), nearly of equal size, and are nearly perpendicular ; the anterior and posterior 

 sides are without costae. 



Of the costaj five or six are prominent, and are distinct to the lower border, the others 

 are less elevated, and are gradually lost upon the surface. P. pelagica, Ag., and 

 P. decemcostata, Roemer, have the costae more oblique, but we think that the species is 

 subject to some variability in this respect, and that they cannot be separated ; 

 Pholadomya nana, Phillips, we also regard as a young example of the same species ; we 

 have arrived at this conclusion from a comparison of the original specimen figured in the 

 ' Geology of Yorkshire,' and placed at our disposal by Mr. Bean. 



Height, 14 lines; length, 25 lines; diameter through both the valves, 12 lines. 



Localities. The specimen forwarded to us is from the Grey Limestone of Scarborough ; 

 it also occurs in the Cornbrash of the same locality. 



PHOLAS PULCHRAUS, Bean. MSS. Tab. XIII, fig. 17. 



Testa subcylindricd, media constricto, lateribus convexis hiantibus, costellis paucis 

 intequalibus radiantibus, umbonibus mediants depressis, et sulco mediano perpendiculariter 

 instructo, laleribus semel plicis longitudinalibus subundulatis et crebris. 



Shell subcylindrical, short, compressed in the middle portion, and convex towards the 

 two extremities, each of which gapes with a considerable aperture ; umbones mesial and 



