284 ME. s. s. BUCKMAX OX [vol. Ixxiii, 



Appendix III. Pal^eoxtology. 

 (a) Introduction. 



In the following pages are given descriptions of certain Lias 

 species which are of importance, either because they are additions 

 to the British fauna, and therefore their recognition may be useful 

 in future work, or because they are of stratigraphical significance. 

 Some few of them happen also to be interesting morphologically 

 and biologically ; but only casual notice of such features is 

 aj)propriate now. 



A few words of explanation may be given here in reference to 

 the descriptions. The proportions are stated alwa^^s in the order 

 proposed in ■' Yorkshire Type Ammonites' ii, p. viii (1913). — Dia- 

 meter in mm., breadth of whorl, thickness, size of umbilicus in 

 percentage of diameter ; S., measurements from actual specimens, 

 ¥., from figures,! ^p^^ from text-statements of author. Other 

 details about descriptive terms will be found in the same place. 



At the close of the descriptions I append a few remarks as to the 

 bearing of the described species on the geological-chronological 

 problem (p. 307). 



[b) Descriptions of Species. 



Family HILDOCERATIDJE. 



G-enus Leptaleoceeas,2 nov. 



Type, X. leptum, sp. nov. 



Definition. — An umbilicate, plate-like, obscurely costate, 

 gammiradiate, stoutl}'' carinate, non-sulcate Hildoceratid. Carina 

 apparently degenerately septicarinate, that is, the cast may not be 

 carinate or so carinate, thus indicating a one-time septate con- 

 dition ; but there is apparently no distinct hollow in the keel : 

 details, however, are obscure. The radial line is of the gamma 

 pattern of Grammocejris, very slightly fiexed lateralh^, produced 

 ventrally, but not excessively. 



Distinction. — The stout carina recalls Tiltoniceras S. Buck- 

 man, ^ but shape, ornament, and radial line are wholl}^ diiferent. 

 There is some suggestion of Grammoceras Hyatt, but this plate- 

 like thin form could not give rise to the stout costates of that 

 lineage. There is a nearer approach to Protogo^ammoceras Spath,'^ 



^ Measurements (especially of small forms) are difficult to obtain accurately. 

 In the case of figures it seems best to lay tracing--paper, and then by a ruler 

 mark diameter and proportions with a sharp pencil. This ensures a true 

 diameter being followed, and saves the plate from the compass-points: the 

 only error may be from the shadow of the umbilical wall. 



'^ AeirraXeos thin, fine, delicate. 



^ ' Yorkshire Type Ammonites ' ii (1913) p. viii. 



•* Q. J. G. S. vol. Ixix (1913) p. 547. 



