

part 1] THE EVOLUTION OF THE LIPABOCERATIdI. & kw 1920 



10. TA<? Evolution of the Lipakocer.vtid.e. By Arthur 

 Elijah Trueman, D.Sc, F.G.S., University College of South 

 Wales, and Monmouthshire, Cardiff. (Read April 17th, 

 1918.) 



[Plates XXI-XXV.] 



Contents. 



Page 

 I. Introduction 247 



II. Historical Notes 248 



III. StratigTaphical Notes 251 



IV. General Evolution 254 



V. Systematic Study of the Genera 257 



VI. Study of Species and Developmental Details 265 



VII. Phytogeny and General Considerations 289 



VIII. Eeferences to Literature 293 



I. Introduction. 



The ammonites dealt with in this paper are characteristic of the 

 uppermost zones of the Lower Lias (Charmouthian), and they are 

 of three general types, namely : — 



(1) A Capricorn form, evolute slender whorls (serpenticone) with stout 



simple ribs. 



(2) An involute form with swollen whorls (sphaerocone), bituberculate, 



generally known as A. striata* or A. becltei. 



(3) A form intermediate between these two. with Capricorn inner whorls, 



the outer whorl swollen, with more numerous slender ribs bearing 

 two rows of tubercles (usually known as A. heterogenes). 



In order to name some ammonites collected at Lincoln, appa- 

 rently similar to those called A. striatus, the relationships of these 

 types were studied; it presently became clear that the classification 

 of these ammonites, and the correlation of the beds in which they 

 occur, needed to be considerably revised, and that such a revision 

 must be preceded by an investigation of all available ammonites 

 composing the family Liparoceratidie. With this in view, a large 

 number of these fossils was collected from practically all the 

 English exposures, their precise horizons were noted, and develop- 

 mental and sutural evidence was examined. The present paper 

 includes the main results of this work. Several new specific names 

 are proposed, but only where this is necessary to define a series : 

 future work may show that many of the intermediate forms 

 mentioned must also receive separate names, but, as this paper is 

 mainly concerned with establishing the lineages and their geological 

 ranges, minute description of species has not been undertaken. 



In the course of this investigation much assistance has been 

 received from other workers. Dr. W. D. Lang kindly placed at 



Q. J. G. S. No. 296. x 



