90 MOLLUSCA FROM THE CRAG. 



2. Leda myalis, CoutUouy. Tab. X, fig. 17, a — c. 



Nucula myalis. Couth. Bost. Journ. Nat. Hist., vol. ii, p. 62, pi. 3, fig. 7, 1839. 



— — Gould. Invert, of Massach., p. 99, 1841. 



— — Bekay. Hist. New York Zool., p. 180, pi. 13, fig. 219, 1843. 



— oblonga 1 Woodward. Geol. of Norf., p. 44, 1833. 



— allied to oblonga. Lyell. Mag. Nat. Hist., New Series, p. 328, 1839. 



— oblongoides. S. Wood. Mag. Nat. Hist., New Series, vol. iv, p. 297, pi. 14, 



fig. 4, 1840. 



— — Morris. Cat. Brit. Foss., p. 95, 1843. 



— — Forbes. Mem. Geol. Surv., vol. i, p. 420, 1846. 



— hyperborea. Loven, sec. Gould. 



Yoldta angularis. Mailer. Ind. Moll. Grbenl., p. 19, 1842. 



Spec. Char. Testa transversa, incequilaterd, elongato-ovatd, tenui ; antice elliptico- 

 rotundatd, postice subrostratd ; laevigata ; dentibus mediocriter angulatis. 



Shell transverse, inequilateral, elonga to-ovate, thin, and externally smooth ; 

 anterior side roundly elliptical, posterior subrostrated ; externally smooth ; teeth 

 moderately angulated. 



Longitudinal diameter, If inch. Height, 1 inch. 



Locality. Red Crag, Sutton and Butley. 



Mam. Crag, Chillesford and Bramerton. Recent, North America. 



This species, like the preceding one, appears in the recent state to be confined 

 to the colder regions of the globe, and as a fossil has been found only in the 

 newer Tertiaries in this country. In the Red Crag I have met with but very 

 few specimens, while at Chillesford it may be obtained in abundance, and is by no 

 means scarce, I believe, in the Estuary portion of the Mammaliferous Crag at 

 Bramerton. It is readily distinguished from L. lanceolata, in being more equi- 

 lateral, the posterior portion is comparatively larger, and it wants the peculiar 

 diagonal ridges which ornament the surface of that shell ; nor does it appear 

 even to attain to such dimensions, my largest specimen being under two inches in 

 its transverse or longest diameter, neither is it ever so thick a shell. A specimen 

 obtained in the Red Crag at Sutton is more elongated or attenuated than those 

 usually found at Chillesford, and it approaches in that character L. limatula of the 

 American Seas (fig. 17, c) ; but that species is rather more elegantly formed, and 

 more rostrated, with a greater curvature at the posterior termination. Our shell is 

 covered with concentric striae or lines of growth, but not in regular ridges, and there 

 is not so distinct a sinus on the anterior side, as in L. lanceolata, although in some 

 specimens a radiating line traverses that side of the shell from the umbo, which line is 

 produced by a slight interruption to the regular curve of the margin : a large corselet 

 is well defined on the posterior side, and the ligamental pit is comparatively larger 

 than in L. limatula. The shell is sometimes thickened in the interior, though never 



