AMMONOIDEA. 73 



It cannot be said that under these circumstances the position of this remark- 

 able group of ammonites generally known as " cretaceous ceratites " is quite clear 

 and it is a great convenience that Douville' in his able paper on the " Classification 

 des Ceratites de la Oraie," has endeavoured to settle the relationship of these forms. 



One of the chief facts elucidated by this author is that the relationship of the 

 genus Buchiceras, Hyatt, is uncertain for the present, and that certainly some of the 

 forms which have been considered to belong to this genus must be separated 

 from it. M. Douville distinguishes two groups : the first, the family of the JPuU 

 eheUid(S, includes the genera StoliczJeaia, ScapUtes, Tissotia, Pulchellia, Neolobiles, 

 and the second includes the genera Flacenticeras and Sphenodiscus which the 

 author includes among the family of the Roplitidce, while Neumayr was of opinion 

 (that they belonged to the family of the Amaltheidce. 



Douville has, therefore, returned to Meek's limitation of the genera Placenti- 

 iceras and Sphenodiscus, but he considers them related to quite a different family 

 to Zittel or Neumayr. Without touching here upon this delicate question, I must 

 •draw special attention to two species of Ammonites of the above group which 

 ■occur in Baluchistan, as one at least apparently represents a new genus. 



If we suppose that in the form described as Sphenodiscus aeutodorsatus the first 

 lateral lobe is represented by the third lobe, counting from the siphonal lobe, as 

 being the largest, then the external saddle is exceedingly broad and divided by two 

 adventitious lobes, the inner one of which is larger than the outer one, and nearly as 

 deep as the first lateral lobe. Of the three branches into which the external saddle 

 Is thus divided, the two outer ones rise from a common basis. To judge from this 

 development of the sutural line, this form must belong to the genus Sphenodiscus. 

 If, on the other hand, the sutural line of Indoceras baluchistanensis is analysed, it will 

 be seen that if the same view were applied to this species, the inner adventitious 

 lobe would be much broader and deeper than the first lateral one — a view which it 

 •would be rather difficult to accept, particularly as regards the sutural line of the 

 largest specimen. If, in the case of the latter, the largest lobe be considered as the 

 first lateral, then the external saddle is divided by a single adventitious lobe into 

 two secondary branches. In this case, however, a fundamental difference would exist 

 between the two species here described, and the latter species could not be consi- 

 dered as belonging to the genus Sphenodiscus, which is characterised by two adventi- 

 tious lobes and a tripartite external saddle. If we examine the genera defined by 

 M. Douville, we notice that the genus most closely related to the above form 

 ■would be the genus Tissotia, Douville, which is characterised by a bipartite external 

 saddle : but on comparing the sutural lines of this genus, as depicted by Douville, I 

 think they differ considerably from the sutural line of Indoceras baluchistanensis ; not 

 only is the secondary lobe much deeper and more independent in the Baluchistan 

 specimens than in any of the species belonging to the genus Tissotia, but there 

 exists also a larger number of auxiliary lobes than in that genus. For this reason 

 I do not think that this form can be considered as belonging to Tissotia. We are 



' Bnlletin de la Society G^olo^ique de Prance, Vol. SVIII, p. 281. 



