164 REPTILIA. 



about 20 cervical vertebrae, slightly more in the trunk region, perhaps four 

 in the sacrum, and not less than 40 in the tail. All the centra are bicon- 

 cave. The cervical ribs are small and distinctly double-headed, while 

 those of the trunk are extremely robust and borne directly by the neural 

 arches, which are almost or completely destitute of transverse processes. 

 About ten anterior caudal vertebras also bear relatively large straight ribs. 

 In the pectoral arch the symphysis of the coracoids is short and the 

 scapulae are widely separated, the interval between the latter being bridged 

 over by a pair of slender clavicles with a minute triangular interclavicle at 

 their point of meeting. The humerus is a little arched and expanded 

 distally, with an entepicondylar foramen, while the radius and ulna are 

 comparatively elongated slender bones. There are only two elements, of 

 unequal size, in the proximal row of the carpus, while five small bones 

 form the distal row, one supporting each digit. The digits increase in 

 length to the third, which equals the fourth, while the fifth is intermediate 

 in length between the first and second. The phalangeal formula is 2, 3, 4, 

 4, 3 ; and none of the phalanges exhibit coudyles, although the distal one 

 is modified by flattening. The pelvis is imperfectly known. The hind 

 limb is larger and stouter than the fore limb, but otherwise very similar ; 

 the digits increase gradually in length from the first to the fourth, while 

 the fifth is shorter again, and the phalangeal formula is 2, 3, 4, 5, 4. 

 Abdominal ribs seem to occupy the whole of the ventral wall of the body 

 between the pectoral and pelvic arches, there being one median longitudinal 

 series sharply bent in the middle line, and at least two paired lateral 

 series. The typical species, Lariosaurus balsami, is known by nearly com- 

 plete skeletons from the black Triassic shales of Perledo, on the shore of 

 the Lake of Como. 



Other genera allied to Lariosaurus are known from the 

 German Muschelkalb, while Mesosaurus, from the Karoo 

 Formation of South Africa, and Stereosternum, probably from 

 an equivalent horizon in Brazil, seem to represent an allied 

 group. In the two last-mentioned genera the scapula and 

 coracoid are described as fused together, while the pubis is 

 pierced by a foramen. The vertebrae and ribs are remarkably 

 thickened by hyperostosis. 



V 



Nothosaurus (figs. 102 A, 105). Larger Triassic Sauropterygians 

 known only by fragmentary specimens, apparently distinguished from the 

 foregoing by the closure of the suborbital vacuity in the palate (fig. 105) 

 and by the presence of short, stout transverse processes on the arches of 

 the dorsal vertebra?. In the pectoral arch (fig. 102 A) the coracoid exhibits 

 a notched and incomplete antero-internal margin, which was evidently 

 completed in an undetermined manner by cartilage. The typical species, 

 Nothosaurus mirabilis, occurs in the Muschelkalk of Bavaria, and has a 



