tiClllSTOCEKAS. 105 



it differs from Prolecanlfix. The two arms of the ventral lobe are widely separated, 

 and there are only throe pairs of lateral lobes and a small umbilical lobe with two 

 pairs of dorsal lobes. The lobes are hastate, and the saddles more rounded and club 

 shaped, us in Prolecanites. The first pair of saddles have dorsal correspondents, and 

 the annular lobe is deep and acute. 



Professor Hyatt's type was never figured, and the existence of any 

 other species Ijelonging to this genus was unknown to him, so it was 

 afterwards either ignored or the species of this group were inchided in 

 other genera. Foord and Crick" recognized the affinity of tliis group 

 with Agathiceras, whicli was estabhshed by Gemniellaro,'' based on tlie 

 type A. suessi Gemniellaro, to include Carboniferous ammonoids with rathei" 

 helmet-shaped whorls, somewhat compressed laterally, witli s])iral orna- 

 mentation, with four external tongue-shaped goniatitic lobes. Karpinsky" 

 subsequently included in this genus Adrian ites Gemmellaro, which differed 

 only in having a longer body chamber and a greater number of lobes. 

 But such a character as this has a much greater significance in the 

 simpler gouiatites than in the specialized ammonites. Thus a difference 

 in number of lobes may always be takeii as indicating generic progress. 

 It thei'efore seems better to leave the genera as Gemniellaro defined 

 them, except as to their systematic position 



Haug** has recentl)^ included in AgatJiiceras two species oi Scliistoceras, 

 8. fultonense Miller and Gurley, and <S'. hUdretlii Morton, which lie assigned 

 to the Glyphioceratidse. On page 105 of the same work Haug redescribes 

 8. hildrethi, and calls attention to the fact that it has one jiair of lobes and 

 saddles more than the tvpe of Aqathiceras, and therefore might represent a 

 new genus descended from Gastrioceras through Farcdec/ocerns. In this he 

 is in jjerfect accord with the writer, except that it was unknown to Haug 

 that the genus 8chistoceras met all these requirements. This genus uniloubt- 

 edly resembles Agathiceras, but appears to differ in the constant number of 

 lobes and saddles; one external lobe divided deeply by a bottle-shaped 

 siphonal saddle, three lateral lobes decreasing in length toward the umbili- 

 cus, a short pointed lobe on the umbilical shoulder; and the internal lobes 

 consisting of a long tongue-shaped undivided dorsal or antisi})honal lobe 

 and two pairs of lateral lobes. There are, then, in all ten external and 



aCatal. Foss. Ceph. Brit. Mus., Pt. Ill, p. 269. « Ammoneen der .Vrtinsk-Stufe, p. 64. 



6 Fauna calc. Fusulina, p. 77. << Etudes sur lea Goniatites, p. 33. 



