214 



THE AMMONITES CALLED SERPENTINUS. 



(plates XIII. , XIV. and xv.). 



C. THOMPSON, B.Sc. (Lond.), 

 Hull. 



When engaged in research in regard to certain ammonites, 

 I asked Mr. Crick of the British Museum (Natural History) if 

 there were any real differences between Reinecke's ' serpentinus ' 

 and Sowerby's ' falcifer.' I was at once gratified by having 

 the Hterature on the subject placed at my disposal by the officers 

 of the museum. 



A glance at Reinecke's beautiful figure was sufficient tO' 

 show that the usual identification of A. serpentinus was in- 

 correct, so I reported to the Hull Geological Society the pub- 

 lished results of Mr. Buckman's work of twenty years ago. 

 Recently a question by Mr. Sheppard, regarding the Yorkshire 

 specimens, set me at work again. 



I have been led to the conclusion that the Yorkshire fossil 

 usually called A. serpentinus is certainly not that species. 

 It might be correct to label it A. mulgravius, Y. and B., but the 

 question is whether that species is really distinct from A. 

 falcifer, Sowerby. 



Mr. Buckman informs me that the authorities of the Whitby 

 Museum have kindly placed Young and Bird's type of A. 

 mulgravius in his hands for study ; that it is a large shell about 

 235 mm. in diameter, with inner whorls very like Sowerby's 

 A. falcifer. 



I have sent him a photograph of Sowerby's species, and he 

 reports to me as follows : — ' The comparison of Sowerby's 

 small falcifer with Young and Bird's large mulgravius is difficult, 

 because the inner whorls of the latter are so much hidden. 

 Both species show in the inner whorls a stage of somewhat 

 strong, broadly-flattened, primary furcating costae preceding 

 the stage of regular, narrow, non-furcating costae. 



In falcifer, the primary costae of the first stage are more 

 distinct than in, mulgravius, and the regular costae of the second 

 stage also appear to be coarser. In falcifer the umbilicus is 

 larger than in mulgravius, and this distinction would increase 

 with age, while the umbilicus of falcifer is certainly deeper, 

 which means that its whorls are thicker than those of A. 

 mulgravius. 



On these data I am inclined to think that falcifer would grow 



. Naturalist 



