136 MOLLUSCA FROM THE GREAT OOLITE. 



rotundo, postice subtruncaio, angulo obliquo obtuso instructo ; margine cardinali subhorizon- 

 tali, inferiore parallelo ; lateribus striis irregularibus tenuibus. 



Shell ovately elongated, compressed and smooth ; umbones depressed, mesial ; anterior 

 border rounded, posterior border somewhat truncated ; an oblique obtuse angle descends 

 from the umbo posteriorly; hinge border horizontal, lower border parallel, the surface 

 with fine irregular longitudinal striations. 



Compared with Quenstedtia oblita, this species is more elongated, the umbones 

 more nearly mesial, and the longitudinal plications are much more delicate, producing a 

 general smoothness of the surface. Length, 2 inches; height, 1 inch. 



Geological position and localities. — Specimens have been forwarded to us from the 

 Grey Limestone bed of the Scarborough Great Oolite ; it also occurs in the Inferior Oolite 

 of Blue Wick upon the same coast, and in the upper division of the Inferior Oolite of the 

 Cotteswolds ; we have also obtained a specimen in the Great Oolite of Minchinhampton, 

 but it appears to be rare at each of these localities. 



Myacites Beanii. Tab. XV, fig. 11a, b. 



Testa ovato-oblongd subcompressd, umbonibus depressis ; antemedianis, area ligamenti 

 angustd, parvd ; margine postico rotundo ; hiante basi et margine anteriore curvato ; superficie 

 sulco lato, superficiali instructo ; plicis longitudinalibus magnis irregularibus. 



Shell ovately oblong, rather short and compressed ; umbones antero-mesial, depressed ; 

 ligamental area small and narrow, the margin posterior to it nearly horizontal ; the 

 extremities of the valves rounded, the anterior extremity being almost closed, the posterior 

 extremity with a lengthened and moderately large aperture ; a superficial and vertical wide 

 depression passes downwards from the umbones crossing the longitudinal plications, which 

 are large and irregular. 



This species is not without a considerable resemblance to Homomya compressa, Ag., 

 but as the latter shell has the anterior side less produced, with a distinct aperture, together 

 with umbones more elevated, we prefer to consider them distinct species ; the short form, 

 depressed small umbones, and fully developed nearly entire anterior border, will also 

 serve to distinguish it from other of the British Myadse. Length, 2\ inches; height, 

 1| inch; diameter through the valves, 1 inch. 



Locality. — Scarborough. 



Myacites securiformis, Phil., sp. Tab. XIII, fig. 15. 



Amphidesma securiforme, Phil. Geol. York., 1, t. 7, f. 10. 

 Pleukomya securiforme, Ag. Etud. Crit., p. 232. 



