258 Two large Ammonites from the Holderness Drift. 



In the Cote d'Orit was found in the Birchi bed, while in. 

 the South German basin it occurred first in that of Geometricum. 

 When found in place in England it should occur in the lower 

 beds of our Oxynotum zone. That it has ever been found in 

 situ in England is doubtful, for no record of it can be found. 

 However, Mr. Sheppard has recently acquired for the Hull 

 Museum, from the Drift of Holderness, a very fine ammonite, 

 which the writer has determined to be a specimen of Hyatt's 

 acceleratum. This determination has been supported by Mr. 

 S. S. Buckman, Mr. G. C. Crick of the British Museum, and by 

 Dr. H. Joly, of the University, Nancy, to whom photographs 

 have been submitted. 



The specimen is the largest one of the species known to the 

 writer, and would have been much larger if it had not lost the 

 entire body chamber. The following are its dimensions : — 

 Largest diameter 

 Width of outer whorl 

 Height of outer whorl (keel to keel) 

 Greatest thickness of outer whorl 

 Width of last whorl but one 

 Width of same overlapped 

 Width of umbilicus 

 An examination of the specimen (fig. 

 consists of five or six whorls (?), that the inner adolescent 

 ones have the characteristic costse or ribs of stellare, but that, 

 they die away gradually in the outer whorl which then becomes- 

 quite smooth. The umbilical shoulders are rounded, large and 

 prominent, so that the umbilicus is deep. The section of the 

 outer whorl is ovate, the flanks converging to the periphery 

 with a gentle curve. Its ventral surface, or periphery, is narrow 

 and sharply defined, while it carries a rounded, depressed, but 

 still prominent keel between two broad but very shallow fur- 

 rows. The keel may be easily distinguished in the figure. 

 It will also be noticed that it is more involute than stellare ;. 

 that is, the outer whorl covers, or overlaps, about one half of 

 the preceding one, while in the last-named, Hyatt writes that 

 the maximum overlap is one-third. The suture lines resemble 

 those of obtusum. 



The second specimen (fig. 2), which is also in the Hull. 

 Museum, has been kindly determined by Mr. G. C. Crick and 

 by Mr. S. S. Buckman as Aster ocer as stellare Sow. This is also 

 a very large ammonite. As it wants by far the greater part of 



Naturalist,. 



317 mm. 



lOI 



95 ,. 

 67 ,. 



34(?) -. 

 100 

 i), shews that it 



