142 Geological Society. 



Pleistocene Homo heidelherc/cnsis. So far as its lower jaw is con- 

 cerned, Dryopitheciis is, therefore, a generalized form from which 

 modern Anthropoid Apes and Man may have diverged in two 

 different directions. 



May 27th, 1914.— Dr. A. Smith Woodward, F.R.S., President, 

 The following communication was read: — 



'On the Development of TmgophyUoeeras loscomhi (Sow.).' 

 By Leonard Frank Spath, B.Sc, F.G.S. 



During his investigation of the Charmouth Lias, Mr. "VV. D. 

 Lang has carefully collected abundant fossil material Avith reference 

 to its exact stratigraphical horizon, and the Author is indebted to 

 him for permission to study the ammonites. In the material, 

 Tragojiliylloceras loscomhi (Sow.) is represented by hundreds of 

 specimens (chieHy young), and a study of the ontogeny of this 

 interesting ammonite forms the basis of the paper. 



A considerable number of specimens were dissected back to the 

 initial chamber or protoconch, and their development was traced 

 in detail. Horizon and history (notably previous interpretations 

 and generic vicissitudes) are also discussed, tables of measurements 

 are given, and the other species of the genus [especiall}^ the pre- 

 ihex Tragopliylloceras numismale (Quenst.) which had long been 

 confused with the post-/i<°.r Tr. loscomhi (Sow.)] are reviewed. 



The evolution of the suture-line was worked out in great detail, 

 and one of the most important points brought out was the demon- 

 stration of a simple Psi I ocer as-like sutm-e-line persisting to a late 

 and post-constricted stage. The speculations regarding the bearing 

 of all the important facts upon the phylogeny of the genus Trago- 

 2)liyUoceras, and upon the connexion of the latter with allied 

 lineages, will prove, it is hoped, of general interest. The develop- 

 ment of the suture-line in Psiloceras and Shacojjliyllifes is given 

 for comparison. 



Since Tragopliylloceras has morphic equivalents in Sliaco- 

 pJiyllites, as well as in Analytoceras, but, by its suture, is moi'e 

 nearly related to Euphyllites and the Psiloceratidse, it is argued 

 that it can more naturally be attached to those Mojsvcirites- 

 descendants that Prof. Diener would group in the Pleuracanthi- 

 tidae than to the typical Phylloceratinae. 



The pre-Triassic ancestors of the Monophyllitln?e are also 

 reA^ewed, and a new" classification of the family Phylloceratidje 

 is proposed. 



