FOSSIL SHELLS OF THE CRAG. 21^7 



Nucula just referred to, yet I cannot help thinking that a 

 few more specimens of each of these would establish the 

 specific identity of the two. The muscular impressions in 

 the crag fossil are rendered indistinct by its internal thicken- 

 ing. 



Nucula ohlon^oides, Nobis, PI. xiv. fig. 4. 



Shell ovato-lanceolate, transverse, sub -inequilateral, posterior side acu- 

 minated, anterior rounded, lunula lanceolate, edge entire. Longitudinal 

 diameter f ; transverse diameter, \\ inch. 



Mammal iferous crag, Bramerton. Red crag, Butley 

 (Suffolk.) 



This Nucula appears to be quite distinct from the preced- 

 ing, for which it has nevertheless been mistaken. I have 

 never seen the young of the ohlonga, but the following cha- 

 racters induce me to regard it as distinct fi:om that species. 

 It is more equilateral ; the difference between the anterior 

 and posterior portions of the ohlonga being at least in the 

 proportion of two to one, while in this there is but a trifling 

 difference. The teeth also are more equally divided than in 

 Nuc. ohlonga. It has a smooth exterior in the place of the 

 diagonal lines which ornament that shell ; there is also no 

 sinus in the anterior margin, and the pallial scar reaches 

 nearly as far as to a line drawn from the ligamental pit to the 

 centre of the ventral margin ; the lines of growth are the 

 only exterior marks that I have been able to detect. 



Nucula semistriata, Nobis, PI. xiv. fig. 5. 



Shell transversely ovate, sub-inequilateral, thin, posterior side acumi- 

 nated and striated transversely, anterior side rounded and smooth, margin 

 entire. Longitudinal diameter ^ ; transverse diameter 1 inch. 



Coralline crag, Sutton. 



I have not seen this from any other locality than the one 

 named, but it is by no means rare at that spot : specimens 

 in size about half that of the above may be obtained in con- 

 siderable numbers. One half of the shell is strongly striated 

 except on the posterior slope, where the strice are nearly ob- 

 literated ; these striae, or rather ridges, with spaces between 

 them forming small furrows, are only on the posterior side, 

 as if that half of the shell had been buried in the sand, while 

 the other had been worn smooth by exposure. The lunula 

 is large, lanceolate, and smooth, with a distinct corselet of a 

 lanceolate form; the muscular impressions are indistinct; 

 and the shell being thin, the transverse fun'ows are visible on 



