Vol. 70.] DEVELOPMENT OF TliAGOPHYLLOCEBAS LOSCOMlil. 339 



come nearest the figure is one from Lyme Regis. There is thus 

 enough evidence to show that the drawing of the French ammonite 

 is incorrect. 



The shell figured by Wright (18S0) is also represented with a 

 wrong apertural view, which led Mr. Buckman (1910) to remark that 

 this form was much thicker than Sowerbv's. In fact, Wright's 

 type is crushed and half -embedded in matrix, and there is no reason 

 to believe that its section originally differed in the least from that 

 of Sowerby's type. Descriptions of TragopJiylloceras loseombi 

 have also been given (without figures) by Tate & Blake (1876) 

 and Dumortier (1869) ; but, since most of the earlier authors 

 neglect dimensions, and since Pompeckj (who for the first time 

 •dealt more fully with these forms, especially the Swabian repre- 

 sentatives of the genus Tragoplij/lloceras) had insufficient material, 

 it will be necessary to redescribe Tr. loseombi in detail after its 

 ontogeny has been traced. 



It should be added that Ammonites loseombi had generally been 

 included in the genus Plijjlloceras. Even Futterer, who established 

 the ' Formenreihe des Pkylloceras loseombi, and traced it back to 

 MonopJiyllites, thus clearly characterizing it as a separate lineage, 

 left it in that genus. But in 1900 Hyatt created the new genus 

 TragopJiylloceras for Quenstedt/s A. JieteropJiyllus mi mis mails, 

 the oldest form of the ' loseombi Formenreihe. ' Prinz, in 1906, 

 objected that the genus, based on a mere mention of the type- 

 species, and created without- adequate description, could not be 

 accepted. In 1907 Vadasz proposed i Pliijllolobites ' for the ' group 

 of Phylloceras loseombi ',' and rejected Hyatt's term, not only on 

 account of insufficient definition, but also on account of its being 

 included in the family Phylloceratidae, whereas Vadasz would assign 

 his ; JPliijllolobites ' to the family Amaltheidse. Since a definition 

 has now been supplied by Mr. Buckman (1912, p. viii), Hyatt's 

 generic name must be adopted for the present lineage ; and, as 

 regards the affinity of the genus TragopJiylloceras with Amaltheus, 

 1 can only say that, after developing young forms of Amaltheus 

 back to the initial chambers, and tracing the evolution of the suture, 

 I agree entirely with Pompeckj (1893, p. 23) and Buckman (1913, 

 2, p. vii), and reject Vadasz's theory. 



III. OxTOGEyy. 



A considerable number of specimens ranging up to 20 mm. in 

 diameter were dissected back to the initial chamber or protoconch, 

 the ' phylembryonic stage' of Dr. Perrin-Smith (1898). This con- 

 sists of the usual transversely-elongate, barrel-shaped chamber, the 

 short and long axes of which measure 0'4-0*45 and 0'55-0"65 mm. 

 respectively. Figs. 1-3 (PI. XLVIII) represent in different 

 positions the initial chambers of three specimens collected 10 feet 

 above the Belemnite-Stone (3 feet above the Lower Limestone) on 

 Black Ven. In Branco's nomenclature fig. 3 a represents the lateral, 

 and fig. 2 c the frontal, aspect ; whereas figs. 1 a & 2 a give the 



