296 FOSSIL SHELLS OF THE CRAG. 



seen, are flatter than those from the mammahferoiis deposit. 

 The specimen mentioned by Sowerby as having been found 

 at Roydon, Norfolk, is an error, there being no crag within 

 many miles of that place. Roydon was at one time the resi- 

 dence of my late friend, the Rev. G. R. Leathes, a well-known 

 collector of the crag fossils, and in this way the mistake pro- 

 bably had its origin. This shell, when found in the mam- 

 maliferous crag, has the valves occasionally in contact, and in 

 a state of preservation which shows that they are regularly 

 and concentrically striated. Specimens are now and then 

 found much thickened internally, leaving two deep, sub-oval, 

 muscular impressions : there is a very small sinus in the im- 

 pression of the mantle on the shorter side, which, on that ac- 

 count, I suppose to be also the posterior side. 



NuculalcBvigata, ' Min. Con.' tab. 192, figs. 1, 2. 



Red crag, Walton Naze. Coralline crag, Sutton. 



This shell has been found plentifully at Walton, but I have 

 only a few small specimens from the coralline crag. It is 

 perfectly smooth externally, free from markings of any kind, 

 and a more transverse shell than the preceding ; my largest 

 specimen measures nearly an inch and a half across its wid- 

 est diameter. The figures of these two shells are so correctly 

 given in the * Mineral Conchology,' that any further represen- 

 tation is unnecessary. 



c. Sub -equilateral y ligamental pit sub-central, edge entire. 



Nucula ohlonga^ ' Min. Con.' tab. 180, fig. 1. 



Red crag, Bawdsey. 



This I presume to be a rare fossil, not having found more 

 than half a dozen specimens, and those all at the above loca- 

 lity : niine are all adult shells, being much thickened inter- 

 nally. The figure above referred to is excellent, but no men- 

 tion is made of the markings which ornament the exterior, 

 consisting of slightly undulating lines running in an oblique 

 direction, and at an angle of about 30° with an imaginary 

 line drawn through its transverse diameter. A shell from the 

 Arctic Ocean, now in the British Museum, figured and de- 

 scribed in the ' Zoological Journal,' vol. iv. p. 359, pi. 9, f. 1, 

 under the name of Nuc. arctica, appears identical with this 

 species ; itis,however, rather thinner and smaller, a difference 

 which may depend upon climate or other incidental causes. 

 There is asmall^iwws in the anterior margin of the crag shell 

 (at least in my specimens), which T did not find in the recent 



