64 tipper jurassic ammonites. [Feb. 1904, 



and in a reference to ' several other ammonites ' in the following: : — 



l o 



' Several other ammonites occur in the same stratum, among them is Am. con- 

 cavus of tab. 105; most of them have lost the shell ; the present is only a 

 cast of the inside ....'; l 



and again in a footnote referring to the said tab. 105. Further, 

 in the description of Am. biplex Sowerby distinctly refers to 

 two figures ; he does not, it is true, actually mention fig, 1 , but 

 he describes it, and says that it came from Suffolk, adding ' Fig. 2 

 is from Barrow.' 2 Additional evidence can be found in the suture- 

 line, which is very complicated and very clearly shown in Am. pli- 

 catilis, while it is only indicated here and there in Am. biplecc ; 

 Sowerby states that ' the septa are acutely sinuated ' in the case of 

 the former, and does not mention them in the case of the latter. 



I hope to deal fully with Am. excavatus at no very distant date. 

 It is, however, necessary to mention it now, as its occurrence with 

 Am. biplex has been adduced by Mr. Blake in support of his 

 suggestion. In one of the quotations given above, Sowerby says 

 that Am. concavus of tab. 105 is found with Am. plicatilis. Un- 

 fortunately, tab. 105 is described as Am. excavatus* and here it 

 must be allowed that Sowerby has made a slip. Still, there is no 

 doubt that he meant Am. excavatus, as Am. concavus is an Inferior 

 Oolite form, and could not therefore occur in the neighbourhood of 

 Dry Sandford and Marcham. jNow the type of Am. excavatus came 

 from Shotover, and we have specimens in the University Museum, 

 Oxford, from the Corallian, which I have identified with it ; there 

 is, therefore, every probability of its occurring along with Am. pli- 

 catilis in the neighbourhood of Dry Sandford and Marcham. Before 

 accepting its recorded occurrence with Am. biplex, I should like to 

 see the specimens which were found together, because I am of 

 opinion that Am. excavatus is confined to the Upper Oxford Clay 

 and the Corallian Beds, while the true Am. biplex is a Kimeridgian 

 form, although several species of Perisphinctes, which are related to 

 it, do occur in the Corallian. 



There is yet another point on which I must beg to differ from 

 Mr. Blake, and that is in regarding Am. variocostatus' as the adult 

 form of Am. plicatilis. The ribs of the inner whorls of the former 

 are much coarser and less numerous than those of the latter, and 

 the suture-line is different. At the same time, I think it highly 

 probable that the ribs of the adult Am. plicatilis suffered a change 

 similar to that which the ribs of Am. variocostatus undergo. — M. H., 

 December 5th, 1903.'] 



1 ' Mineral Conehology ' vol. ii (1818) p. 149. 



2 Ibid. vol. iii (1821) p. 168. 



3 Thid vol ii flftlS^ r> R 



Ibid. vol. ii (1818) p 



