BIVALVIA. 139 



condition of the large and well-known Panop&a gibbosa, Sow., a species in which the test 

 has not been observed, and which in the Cotteswolds and West of England, is procured in 

 the upper portion of the Inferior Oolite; our small example is more than usually elongated, but 

 the species differs very much in this particular, and we possess examples from the Inferior 

 Oolite in which the posterior side is fully as much elongated. The large elevated umbones and 

 tumid anterior side of the shell, serves to distinguish it from another Inferior Oolite species 

 hitherto undescribed, and for which it has not unfrequently been mistaken ; the older or 

 fully developed specimens of Myacites gibbosus are invariably shorter and more ventricose. 

 The shell figured by d'Archiac represents a specimen of medium size ; the Homomya gibbosa, 

 Ag., ' Etud. Grit. Myes/ pi. xviii, is our Myacites Vezelayi, a shell which never occurs in 

 the Inferior Oolite. 



Dimensions of the small Yorkshire example. Height, 13 lines; length, 25 lines; 

 diameter through both the valves, 1 1 lines. 



Locality. Scarborough. 



MYACITES ^QUATUS, Phil. Sp. Tab. XII, fig. 15. 



MYA JJQUATA, Phil. Geol. York., 1, t. 11, f. 12, (junior.) 



Testa ovato-tumidd, umbonibus magnis, elevatis antemedianis, latere antico producto, 

 postico attenuate ; margine superiore concavo, declivi ; basi elliptico curvato. 



Shell ovate, tumid ; umbones large, elevated, slightly compressed, and placed anterior 

 to the middle of the valves ; anterior side produced, middle portion ventricose, posterior 

 side rather compressed and attenuated ; lower border curved elliptically ; the sides of the 

 valves have fine irregular striations. Our species possesses some general resemblance to 

 Pleuromya tenuistria, Ag., but it is more lengthened, and the posterior side is more 

 attenuated, the superior border having a greater declivity. 



We believe that the small shell figured by Phillips under the name of Mya cequata, is 

 the young condition of the larger specimen we have figured, in which the posterior side 

 has with increase of growth become somewhat more elongated. 



Height, 12 lines; length, 20 lines; diameter through both the valves, 10 lines. 



Locality. Scarborough, in the Grey Limestone. 



GRESSLYA PEREGRINA, Phil. Sp. Tab. XV, fig. Ba, b. 



Syn. UNIO PEREGIUNUS, Phil. Geol. York., 1, t. 7, f. 12. 



GRESSLYA ERYCINA, Ag. Etud. Grit. Myes., p. 214, t. 14, f. 19. 

 GRESSLYA CONCENTRICA, Ag. Etud. Grit. Myes., p. 213, t. 14, f. 10 15. 

 PEREGRINA, Morris. Cat. Brit. Foss., 2d ed., 1854, p. 203. 



Testa ovato-cordiformi, tenui, umbonibus antemedianis subdepressis, anticc productd et 



