154 REPORT — 1841. 



the surface of the tooth ; they form a slight curve at their origin, with the 

 concavity directed towards the base of the tooth ; then proceed straight, and 

 at the periphery bend upwards in the contrary direction. The diameter of 

 the calcigerous tube is sj^q*'^ °^ ^^ ^'^^^ ' ^^^^ breadth of the interspace of the 

 tubes is g^jjjth of an inch. The crown of the tooth is invested Avith a simple 



coat of enamel. 



This microscopic examination of the structure of the teeth, which I have 

 been enabled to make by the kindness of Mr. Stutehbury, satisfactorily esta- 

 blishes the distinction between the Saurian of the Bristol conglomerate and 

 the reptiles of the later member of the new red sandstone system in War- 

 wickshire, which I have described under the name of Lubyrinthodon. 



Palceosaurus, Riley and Stutehbury. — In the formation which contained 

 the jaw and teeth of the Thecodontosaurus, two other teeth were separately 

 discovered, differing from the preceding and from each other ; the crown of 

 one of these teeth measuring 9 lines in length and 5 lines in breadth. It is 

 compressed, pointed, with opposite trenchant and serrated margins ; but its 

 breadth as compared with its length is so much greater than in the Thecodonto- 

 saurus, that Dr. Riley and Mr. Stutehbury have founded upon it the gemxsPa- 

 lceosaurus,and distinguish it by the specific name oiplatyodon, from the second 

 tooth, which they refer to the same genus under the name of Palceosaurus 

 cylindrodon. The portion of the tooth of the Palceosaurus cylindrodon which 

 has been preserved, shows that the crown is sub-compressed and traversed by 

 two opposite finely-serrated ridges, as in the Thecodontosaurus and Rho- 

 palodon ; its length is 5 lines, its breadth at the base 2 lines. 



The vertebrae associated with these teeth are biconcave, with the middle 

 of the body more constricted, and terminal articular cavities rather deeper 

 than in TeleosaWrus ; but they are chiefly remarkable for the depth of the 

 spinal canal at the middle of each vertebra, where it sinks into the substance 

 of the centrum ; thus the canal is wider, vertically, at the middle than at the 

 two ends of the vertebra : an analogous structure, but less marked, obtains in 

 the dorsal vertebrae of the Rhynchosaurus from the new red sandstone of 

 Shropshire. 



Besides deviating from existing lizards in the thecodont dentition and bi- 

 concave vertebrae, the ancient Saurians of the Magnesian conglomerate also 

 differed in having some of their ribs articulated by a head and tubercle to 

 two surfaces of the vertebra, as at the anterior part of the chest in Crocodiles 

 and Dinosaurs. The shaft of the rib was traversed, as in the Ichthyosaur 

 and Rhynchosaur, by a deep longitudinal groove. Some fragmentary bones 

 indicate obscurely that the pectoral arch deviated from the Crocodilian and 

 approached the Lacertian or Enaliosaurian type in the presence of a clavicle 

 and in the breadth and complicated form of the coracoid. The humerus ap- 

 pears to have been little more than half the length of the femur, and to have 

 been, like that of the Rhynchosaurus, unusually expanded at the two extre- 

 mities. The femur is thus described by the discoverers of the present the- 

 codont reptiles : — 



" Two femurs, in a tolerable state of perfection, have fortunately been 

 found ; one, of the right side, exhibiting nearly the whole of the bone, the 

 inferior condyles only wanting ; the other is the left, and exhibits the con- 

 dyles, but is very imperfect at the superior extremity. The first mentioned 

 measures 10 inches in length ; from the head to the middle of the trochanter 

 3 inches j^ths ; from the trochanter to the inferior condyle 5 inches /^ths. 

 In the left femur the transverse diameter of the condyles is 2 inches y%ths ; 

 the centre of the cylinder 1 inch. They are curved in two directions upon 



