ES 800 a 
back near the orbits. Dentition thecodont, teeth most= 
ly very long and delicate; small teeth on vomer 
(pre-vomer). Vertebral centra very heavy, amphi- 
coelous. Two sacrals not coalesced. Singleheaded mo- 
vable ribs on all presacrals except the atlas, those 
of the thoraco-lumbar region very heavy. Abdominal 
ribs present. Tail very long. Limbs adapted for 
swimming. Clavicles and inter-clavicle well-de- 
veloped, no separate pre-coracoid, coracoid with 
foramen. 
Pelvic elements not codssified, pubis with foramen 
or notch. Carpus and tarsus completely ossified. 
Digital formula manus 2, 3,4, 4,3, pes2,3,4, 5, 3. 
No osseous dermal scutes. 
Mesosaurus, Gervais 1867—9. 
Pubis with notch, presacral vertebrae about 29. 
tenuidens, Gervais. 
Permian of South Africa. 
brasiliensis, Me Gregor, 1906. 
Head longer than neck, cervical vertebrae 11, thoracos 
lumbars 18. Permian of Brasil. 
Stereosternum, Cope, 1885. 
Pubis with foramen head and neck of equal lenght, pre- 
sacral vertebrae about 34. 
tumidum, Cope, 1885. 
Cervicals 12, thoraco-lumbars 22. Permian of Brasil. 
Description of Mesosaurus brasiliensis 
Skull. 
The material comprises six more or less complete skulls, Of these 
the largest, which is ill-preserved, measures 110™". in length ; 
two others, about 85"".; and one 78"™. The general form of 
the skull with its long snout and needle-like teeth is well-shown 
in Plate IV. (Figs. 6, 7 and 8.) The cranial portion proper is very 
short, the large orbits placed far posteriorly and directed dorso-laterally, 
The nostrils are placed far back, as in Phytosauria and Ichthyosauria, 
and are widely separated by the nasal bones. Owing to crushing of 
material it has been impossible to discern definitely the structure 
