SAUROPTERYGIA. 



165 



skull attaining a length of 0'35 m. Nearly all known remains of the genus 

 were obtained from the Muschelkalk-series of Germany and France. 



Plesiosaurus (figs. 102 B, 106 A D, F, H, i). Known by several nearly 

 complete skeletons from the Lower and Upper Lias of Europe. The head 

 is small, the neck very long, the tail also of moderate length. The symphy- 

 sis of the mandible is short and the anterior teeth are somewhat enlarged. 

 The interpterygoid and suborbital vacuities are small but distinct on the 

 palate. There is a "columella" (epipterygoid) rising to the prefrontal. 

 The number of cervical vertebrae varies between 30 and 40, and the neck 

 is stiffened by the overlapping of the hatchet-shaped cervical ribs, which are 

 all double-headed. The trunk in front of the sacrum comprises about 20 

 vertebne, and the sacrals seem to be two in number ; these all bear single- 

 headed ribs. The number of caudal vertebrae is uncertain, but there must 

 sometimes have been not less than 40 ; most of them bear short caudal 



pmx 



FIG. 105. 



Nothosaurus mirabilis; restoration of palatine aspect of skull, one-quarter nat. 

 size. M. Triassic (Muschelkalk) ; Bavaria, a, hinder extension of pterygoid ; 

 6, suture of same with quadrate; mx., maxilla; war., posterior nares; oc., 

 occipital condyle; pal., palatine (possibly with ectopterygoid at hinder 

 end); pmx., premaxilla; pt., pterygoid; qu., quadrate; vo., vomer. (After 

 Lydekker.) 



ribs and chevron bones of which the right and left halves are not fused 

 together below in the median line. In the pectoral arch the coracoids are 

 antero-posteriorly elongated, with the long symphysis produced a little 

 forwards in front of the glenoid cavity for the humerus ; and the scapulae 

 do not meet in the middle line below, but are distinctly extended ventrally 

 beneath the outer borders of the large bilaterally-symmetrical triangular 

 plate which represents the clavicular arch (fig. 102 B). The humerus is 

 much expanded distally, but without trace of an epicondylar foramen or 

 groove ; the radius and ulna are both a little longer than broad. There 

 are four elements in the proximal, and three in the distal row of the 

 carpus, while the fifth metacarpal is in direct contact with one of the 

 former. The phalangeal formula is variable, but seems to be 4, 6, 9, 8, 7, 



