4^8 MR. S. 8. BTJCKMAN ON THE GROUPING OP SOME [Aug. 1 898, 



Genus Lioceras, Hyatt, 

 [Type : Lioceras opalinum, Eeinecke.] 



The species which I placed under this generic name in my 

 monograph will have to undergo considerable revision. Though 

 they have a certain similarity of external form, they differ appre- 

 ciably in the trend of their costae (or striae) and to a certain extent 

 in septal details. 



Further, there are several species similar to opalinum, even to the 

 possession of the fine hair-like striae; but on strict examination 

 these species are found to have differences of rib-flexure. In some 

 instances they existed at different dates, in other cases they were 

 contemporaneous ; but they have caused great geological confusion. 



And then the question arises, which among these very similar 

 forms is really the true opalinum ? Por it is qpalinum aud its 

 ancestors which constitute the genus Lioceras. And E,einecke*s 

 figure of opalinum is, in connexion with such similar forms as these, 

 very difficult to interpret, as the drawing is by no means exact 

 enough for the purpose. 



The subject wiU be more definitely treated in the forthcoming 

 part of the monograph, but I would now note that the specimen 

 figured as opalinum in that work, pi. xiii, figs. 1 & 2, will be 

 separated from opalinum as a distinct species by the name opalini- 

 forme^ and also as a distinct genus. This will explain the use of 

 the term opaliniformis in the hemeral Table (I) ; and in the 

 genealogical Table (II) it is entered as Lioceratoid. 



Genus Brasilia,^ S. Buckm. 

 FType: Brasilia hradfordensis,^ S. Buckm.] 



The flexure of the rib is the distinguishing character of this 

 genus : the curvature is different from that which obtains in the 

 opalinum 'gvoxx^ — true Lioceras, 



Genus Geaphoceras,^ S. Buckm. 

 [Type : Graplioceras v-scriptum,^ S. Buckm.] 



The V-shaped costae which suggested the specific name separate 

 the type and other species as a genus distinct from any hitherto- 

 named genus of the family Hildoceratidae. 



^ In honour of M. Louis Brasil, who has done good work among the 

 Jurassic ammonites of Normandy. 



2 Monogr. Palaont. Soc. ' Inf. Ool. Amm.' pt. i (1887) pi. iv, figs. 5 & 6. 



^ ypcKpos, what is written, a letter. 



* Op. supra cit. pt. ii (1888) pi. x, figs. 5 & 6. 



