94 BLUE CHALK MARL. 



Numerous fragments of this species occur at Eingmer, Norlington, and 

 Laugh ton. 



The specimen dehneated, tab. xxiii. fig. 12, is probably a variety, since 

 the costffi are larger and less numerous than usual ; the foliaceous septa 

 are seen in the upper part of this specimen. 



24. Nucula pec^m«ia. Tab. xix. figs. 5, 6. 9. (Min. Conch, tab. 192, 

 6,7.) 



Transversely elHptical, elongated, convex, longitudinally striated ; 

 striae diverging from the beaks to the margin, decussated by fine trans- 

 verse Hues ; posterior side truncated ; lunette depressed, cordiform ; margin 

 ■serrated. . 



The surface of this 'elegant shell is marked with longitudinal strife, 

 crossed by transverse Hnes, and separated by 'fine sulci ; the latter are but 

 obscurely shewn in perfect specimens, but are very conspicuous in those that 

 are worn. In the adult shell the lines of growth are numerous and distinct. 

 The constituent substance of these fossils is a light fawn-coloured 

 carbonate of lime ; their cavities being filled with argillaceous ironstone, 

 wliich forms bold casts when the shell is decomposed. The lunette at 

 the truncated extremity is large, and characteristic of the species. The 

 situation of the teeth of the hinge, and the muscular impressions, are 

 shewn in the casts. 



This shell occurs in almost every locality of the blue marl, to which it 

 is considered to be pecuUar. 



Tab. xix. fig. 5. A cast exhibiting the impression of the hinge, the 

 serrated margin, and the eminences formed by the deep muscular im- 

 pressions. 



Figs. 6 and 9, are different views of a perfect shell. 



25. Nucula ovata. Tab. xix. figs. 26 and 27. 



Transversely ovate, rather depressed, obscurely striated transversely; 

 lunette slightly impressed, cordate, elongated ; margin entire. 



Tliis species of nucula is of a transverse oval form, and its surface is 

 nearly smooth ; the striee being very minute. The lunette is cordiform, 

 very shallow, and elongated. 



