290 Structure of the Fossil Saurians. 



and there is also the rudiment representing the fifth, as in 

 the Crocodile. The first bones of the toes almost exceeded 

 the leg: bone in length. I have obtained two vertebras 

 of the pelvis of this animal. There are 15 vertebrae of the 

 back, and 23 of the tail may also be reckoned. The end of 

 the tail, however, and the fore part of the trunk, are wanting. 

 On a comparison with the Aeolodon, this Rhacheosaurus must 

 have measured 5j Paris feet. The skin consisted of much 

 thinner and lighter scales than those of the Crocodile. I am 

 acquainted with but one species, which I name R. gracilis. 



3. Pleurosau'rus. 

 The remains on which I establish the genus Pleurosaurus 

 I found in the collection of Count Minister. As in the Rha- 

 cheosaurus, the head, the neck, the apparatus of the breast, 

 the fore limbs, and the tail, are wanting. The vertebra?, 

 together with their spinous processes, are much crushed ; as 

 far as the pelvis they were furnished with ribs. The abdomen 

 also had its ribs : these were in pairs, and consisted of a 

 longer and shorter, which lay near or upon each other, and 

 of which it is probable the longer only were connected with 

 the ribs of the back. The relation of the length of the leg 

 with that of the thigh is as two to three. The phalanges of 

 four toes are perceived. The skin, it appears, was thin, scaly, 

 and light. The size of the animal could not have much 

 exceeded 1 ft. The name is formed from pleura, a rib. I 

 know only one species, which I name P. Goldfussii. I have 

 stated more particulars of this animal in the Acts of the 

 Academy of Leopold and Caroline. This Saurus is probably 

 the same which Count Minister (Zcit. f Geog., Geol., &c, 

 1829) refers to a new animal, allied to the Chameleon. 



Geosau'rus.* 

 Privy Counsellor Von Sommerring has, in the Transactions 

 of the Royal Academy of Sciences of Munich made known 

 the existence of a Saurian, which he names the Lacerta 

 gigantea. Baron Cuvier declares it to be a new subgenus 

 between the crocodiles and monitors, which he names Geo- 

 saurus. I, however, consider this animal to be no more 

 referrible to the Crocodiles or Monitors than the foregoing. 

 The form of the head, on the whole, more resembles that of 

 the Monitors. The single bones of the head, however, are 

 often differently formed from those of Monitors, and approach 

 nearer to those of the Crocodiles. The sclerotica, as in the 



* This Saurian, as well as the following, which have no number prefixed, 

 are only placed provisionally in this division until their toes are more 

 fully ascertained. 



