j>art 4] evolution of the lipakoceratidje. 249 



-and, although Schlcenbach has more recently studied the type- 

 specimens, 1 it is still uncertain precisely which species is covered 

 by the name A. capricornus, and for the present it is perhaps 

 better not to use the name. When the name A. maculatus has 

 been emplo} T ed it has nearly always been misapplied, as, for example, 

 by Wright and Quenstedt ; while the term A. latcecosta. which 

 -covers a species that is related to many of our English capricorns, 

 has until lately been very little used. 



All the above-mentioned writers, while they often figured sutures 

 of these ammonites, made no use of the suture as a means of 

 identification. F. von Hauer, 2 who described another Capricorn 

 in 1854, pointed out the features in its suture by which it might 

 be distinguished from the ammonites that it resembled. Apparently 

 his remarks have hitherto been overlooked. 



In 1867 Hyatt proposed the three genera Jlicroceras, Andro- 

 cjipioceras, and Liparoceras, to include respectively the Capricorn 

 ammonites, the ammonites of the heteroqenes-ty\>e, and those of 

 the striatus-tvpe. Such an arrangement made generic identifica- 

 tion simple, since each genus was comparatively distinct. Wright 

 concluded, however, from a study of these fossils, that A. Ixenleyi 

 was descended from a Capricorn form, A. latcecosta, and similarly 

 that A. heterogenes had inner whorls resembling those of A. capri- 

 cornus (8, p. 370). That is to say, Wright recognized two genetic 

 series, each of which included Capricorn and heterogenes-like forms. 

 While Wright also noted that the outer whorl of A. heterogenes 

 resembled A. striatus, he did not suggest that this latter ammonite 

 was a further advance along the same line of descent, because 

 the inner whorls of A. striatus show no trace of Capricorn orna- 

 mentation. E. Haug 3 also noticed the smooth inner whorls of 

 A. striatus, and suggested that they resembled A. qlobosus; still 

 more recently Prof. J. Perrin Smith has included A. bccliei and 

 similar species with the Polymorphinse, separating them from the 

 remainder of the Liparoceratida?, presumably for the same reason. 4 



Mr. S. S. Buckman suggested, however, in 1891, 5 that ammonites 

 of the A.-striatus type are descended from Capricorn ammonites, 

 the Capricorn style of ornamentation being omitted in the develop- 

 ment of advanced members of the series as the quickest method of 

 producing shells of globose form. This conclusion is supported by 

 the details to be given later. Mr. Buckman accordingly revised 



1 Schloenbach studied Schlotheim's type-specimens of A. capricontus, and 

 said that they were identical with A. maculatus Quenstedt. See U. Schlcen- 

 bach, ' Ueber den Eisenstein des Mittleren Lias, &c.' Zeitschr. Deutsch. Geol. 

 Gesellsch. vol. xv (1863) p. 465 ; but this is not sufficiently definite to be of 



walue. 



2 ' Beitriige zur Kenntniss der Capricornier der (Esterreichischen Alpen ' 

 Sitzungsb. K. Akad. Wissensch. Wien, vol. xiii (1854) p. 94. 



3 ' Ueber die Polymorphidae, &c.' Neues Jahrb. vol. ii (1887) p. 103. 



4 J. P. Smith in Eastman- Zittel, ' Text-book of Palaeontology ' 2nd ed. vol. i 

 (1912) p. 67. 



5 S. S. Buckman, 'Monograph of the Inferior Oolite Ammonites * Pala?ont. 

 /Soc. p. 289 (footnote). 



x2 



