E. S. Willbourn — The Pahang Volcanic Series. 447 



Tig. 13 *) affords additional evidence. In each of these two forms 

 the high median saddle of the first suture gives place in the second 

 suture to a broad, shallow median lobe, which is in each case divided 

 by a median saddle in the third suture. The development of folioies 

 and their arrangement in the adult suture point to a close relationship 

 between Polymorphites and Cymbites. The length of the body- 

 chamber in the two genera is about half a whorl, although Cymbites 

 appears to have a different form of mouth from that of Polymorphites. 2 



wvVV 



Fig. 13. — Sutural development of Cymbites globosus 

 (after Branco). 



Cymbites Icevigatus is in some respects intermediate between 

 C. globosus and Polymorphites in being more e volute, feebly costate, 

 and often having a slightly angular venter, which is not developed, 

 however, until a diameter of 12 mm. is reached. 3 It is thus extremely 

 probable that Polymorphites is derived from a form resembling 

 Cymbites globosus, possibly through C. Icevigatus. Such a position 

 near the radical stock would account for the primitive characters 

 noted, and for the amount of variation in different representatives of 

 the genus. 



III. — The Pahang Volcanic Series. 



By E. S. Willbourn, B.A., Assistant Geologist, Federated Malay States. 



(WITH PLATE XXIX AND A MAP, PLATE XXX.) 



Introduction. 



fMHE name Pahang Volcanic Series was given by Mr. J. B. 

 I_ Scrivenor to those eruptive and intrusive rocks of the Malay 

 Peninsula which are older than the Mesozoic granite, and the rocks 

 were described by him in The Geology and Mining Industries of Ulu 

 Pahang, 1911, ch. xi. As the name implies, the series is most 

 strongly developed in Pahang, but it is also developed to a greater 



1 Af ter W. Branco, Beit. Entwick. foss. Ceph., Th. i, tab. xii, 1879. 



2 E. Dumortier, D6pots Bassin Rhone, pt. iii, pi. xviii, figs. 3, 4, 1869. 



3 A. Hyatt, "Genesis Arietidag": Smithsonian Contributions, No. 673, 

 pi. viii, fig. 10, 1889. 



