INTRODUCTION. vii 



Lariosaurus balsami has been described by Boulenger * ; this shows that the limbs 

 were not paddle-like, the propodial bones being relatively long, and the nranus and 

 pes not having undergone any increase in the number of phalanges. In the shoulder- 

 girdle the clavicular arch is strongly developed, but the scapula? have no well-developed 

 ventral ramus, and the coracoid is not expanded as in the later Plesiosauria. No 

 ossified precoracoid has been found in any of the primitive Sauropterygians, but, as 

 Seeley has shown f, it is probable that a precoracoidal cartilage existed: the dis- 

 appearance of this element is probably due to the great development of the clavicular 

 arch, which is itself replaced functionally in many of the later Plesiosaurs bv the 

 ventral rami of the scapula?. 



The pelvis in the Triassic Sauropterygia differs considerably from that of the later 

 forms. Thus the ilium, ischium, and pubes meet in the acetabulum in a triradiate 

 suture in the normal way (see Part I. text-fig. 64, p. 114), there is a pubic notch or 

 foramen, and the pubes and ischia are not greatly expanded ; the enormous plate-like 

 pubes and ischia of forms like Pliosaurus have been secondarily acquired in correlation 

 with the entirely aquatic mode of life — the enlarged pubes being mainly for the 

 support and protection of the abdominal viscera, the ischia for the attachment of 

 swimming-muscles. 



Concerning the relationships and origin of the Sauropterygia many different opinions 

 have been expressed. Many writers {e.g., Baurjand Furbringer §) have considered 

 that there is close relationship with the Chelonia, but the many objections to this 

 view which have been summed up by Williston || and Hay ^[ render it untenable. 

 Broom ** considers that the group sprang from a land ancestor somewhat resembling 

 Sphenodon, but with the supratemporal fossa alone developed; Jaekel ff, on the other 



* Trans. Zool. Soc. vol. xiv. (1896) p. 1. 

 t Proe. Eoy. Soc. vol. 5-1 (1893-4), p. 157. 



± "The Phylogenetic Arrangement of the Sauropsida," Journ. Morph. vol. i. (18S7) p. 97. 

 § " Zur vergleichenden Anatoinie des Brustscbulterapparates und der Schultermuskeln," Jenaisehe 

 Zeitschr. vol. xxxiv. (1900) p. 335. 



|[ "The Skull of Brachauclienius, with Observations on the Relationships of the Plesiosaurs," Proe. U.S. 

 Nat. Mus. vol. xxxii. (1907) pp. 486-9. 

 % 'The Fossil Turtles of North America' (1908), p. 30. 



** "Observations on the Structure of Mesosaurus" Trans. S. African Phil. Soc. vol. xv. (1904), p. 103. 

 ft " Ueber das System der Eeptilien," Zool. Auzeig., Jabrg. xxxv. (1910) p. 324. 



