72 FAUNA OF BALUCHISTAN. 



sensu stricto and Sphenodiscus. The latter genus has been characterized by its 

 author as follows : 



" Shell with periphery cuneate ; umbilicus very small ; volutions each almost 

 entirely embraced by the succeeding one ; septa with the first five or six lateral 

 sinuses provided with only a few short, nearly simple, obtuse divisions, while the 

 others are simple and usually broadly uniform at the ends." Meek considers 

 Sphenodiscus as a subgenus of the genus Flacenticeras, the most marked features of 

 which are according to him, the lenticular form of the shell, the very narrowly 

 truncated or sharply cuneate periphery ; broad, deeply embracing volutions, sagit- 

 tate aperture, small umbilicus and numerous not very large or very deeply divided 

 lobes and sinuses, arranged in undulating series across each side, the lateral lobes 

 increasing in size to the third one, which is always the longest of the entire 

 series, and those beyond in all cases regularly decreasing in size to the umbilical 

 margin. 



Owen has considered Ammonites lenticularis as the type of the genus Spheno- 

 discus, but Meek further remarks that it also probably includes Ammonites 

 pierdenalis, von Buch. 



In his memoir on the Ammonitiden der Hilsbildungen' Neumayr apparently 

 takes a different view. He considers the following species — 



Ammonites placenta, Dek., 



„ guadaloupce, Boemer., 

 „ orbiguyanus, Geinitz., 



which Meek has considered as types of his subgenus Flacenticeras, as types of 

 this auihor's subgenus Sphenodiscus, and those forms which Meek has consider- 

 ed as types of the latter genus, represent the types of Neumayr's new genus Engono- 

 ceras. The reason of this was apparently, that Neumayr considered Flacenticeras 

 a barbarous term which ought to be suppressed, but it cannot be said that Neu- 

 mayr's suggestions were particularly well chosen. In fact, serious objections might 

 be raised against changing a name, simply because it is grammatically incorrect. 



ZitteP has apparently not accepted Neumayr's views, as he acknowledges the 

 independence of the genera Sphenodiscus, Meek, and Flacenticeras, Meek, but he 

 considers the first one as a subgenus of the genus Buchiceras, Hyatt, which accord- 

 ing to Neumayr belongs to quite a different section of the genus Amaltheus, viz. 

 those with a normal number of lateral lobes, while Sphenodiscus and Engonoceras 

 represent the section with a larger number (three and more) lateral lobes. 

 According to Zittel the subgenus Buchiceras comprised all the forms with a 

 normal number of lobes, the external saddle of which, although being broad, was 

 not subdivided by adventitious lobes. 



The genus Sphenodiscus includes those forms in which the external saddle was 

 divided by adventitious lobes into three branches of unequal size. 



* Flacenticeras forms an entir-ely independent genus according to Meek. 



' Palseontographioa, Vol. XXVII, p. 140. 

 ' Handbuoh der Palaontologie, p. 450. 



