GASTEROPODA. 39 



but are derivatives from some other formation. As they approach species figured in Dr. 

 Speyer's work from the Oligocene of Cassel, in Germany, nearer than they do to any others 

 that I can find figured and described, I suspect that they have been introduced from some 

 Upper Eocene or Oligocene formation in North-Eastern Norfolk, through which a stream 

 flowed which discharged into the estuary of the Fluvio-marine Crag. The probability of 

 such a thing is strengthened by the circumstance that the chalk disappears below the 

 water-line of the country immediately east of the Bramerton Crag Pit, and by the Lower 

 Eocene having been pierced at Yarmouth and found to extend to a depth of 526 feet 

 below the sea level. 1 



The specimens in question comprise 



1. CERITHIUM DERIVATUM, S. Wood. Figured in margin. 



Locality. Fluvio-marine Crag, Bramerton. 



Two specimens of this species were among the shells sent by Mr. Reeve. One of 

 these was so much worn and mutilated as to be recognisable with great difficulty, but 

 the other, which is that represented in the zincograph, is in tolerable condition ; for 

 though it has lost its apex, that is a thing not unfrequent with 

 fossils of this genus, even where no suspicion of derivation attaches 

 to them, and the surface is but little worn. It resembles the 

 representation given by Dr. Speyer of Ceritldum Descoudresi, from 

 the Upper Oligocene, ' Cassel Tert. Conch.,' Taf. xx, fig. 20, b ; 

 but his figure shows six distinct transverse or spiral lines, whereas 

 the Bramerton specimen shows but four on the lower, and not so cerithium derivat, & Wood, 

 many on the upper whorls. With that distinction I have been enlarged \. 



unable to refer the specimen to Dr. Speyer's species, but as the number of transverse 

 lines in this genus is not a constant character, it may, nevertheless, belong to it, and 

 further specimens would determine that question. I haye accordingly assigned to it 

 provisionally the above name in order to distinguish its derivative origin. The specimens 

 will be preserved in the Norwich Museum. 



2. ODOSTOMIA ? DERIVATA, S. Wood. Figured in margin. 



Locality. Fluvio-marine Crag, Bramerton. 



Several specimens of this shell were among the quantity already mentioned as sent 



1 Prestwich, in ' Quarterly Journal of the Geol. Soc./ vol. xvi, p. 450. 



