382 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 31, 



caudal vertebrae of the Mosasaurns, with their aiichylosed haemal 

 arch, is well-kiio\vn and sufficiently marked. That the vertebrae in 

 question have not formed part of a tail of a reptile, is shown by 

 the entire absence of hypapophyses as well as haemapophyses from 

 the under surface of their centrum (see fig. 2) ; from the side of 

 w^hich, however, a large transverse process, probably a parapophysis 

 {d, fig. 1), has projected. That they had not come from the cervical 

 or abdominal regions of the spine of the Mosasaur was satisfactorily 

 proved by examples of vertebrae of the true Mosasaiums Maximilianiy 

 from both those regions of the bod}^, w^hich were obtained by Prof. 

 H. Rogers from the same deposits and locality, and formed part of 

 the collection compared. The diiference in the forms and propor- 

 tions of the vertebrae in question with corresponding ones of the Mo- 

 sasaurns having diapophyses from the sides of the centrum, and no 

 hj-jDapophyses, is so great, that I cannot refer them with any probabi- 

 lity to the same genus : they might belong to the Mosasauroid genus 

 Leiodon ; but in the absence of the confirmatory evidence of the teeth, 

 it seems preferable to refer the vertebrae in question to a new genus, 

 which I propose to call ' Macrosaurus,' from the length of the body 

 indicated by the proportions of the vertebrae. I have no doubt, 

 however, that it appertains to the Mosasauroid family of Lacertian 

 reptiles, not to the procaelian Crocodilia. 



The remains of the true Mosasaurns in Prof. H. Rogers's collection 

 included teeth, numerous vertebrae, bones of the extremities, and the 

 characteristic part of the cranium figured in PI. X. fig. 5. The teeth 

 and the vertebrae showed the species to be identical with that so well 

 defined from the European Mosasaurns Hoffmanni by Prof. Goldfuss, 

 under the name of Mosasaurvs Maocimiliani. The lacertian affinities 

 of this singular genus of gigantic Sauria are well illustrated by the 

 basioccipital, PI. X. fig. 5 — a bone of the cranium of the Mosasaur 

 which has not before been described or figured. It presents, as in 

 other Sauria, a convexity tow^ards the atlas, but sends downwards 

 from its under surface two diverging hypapophyses — a character met 

 with only in the Lacertian Sauria, and not in any of the Crocodilians. 

 The difference between the Crocodilian and Lacertian Reptiles in this 

 respect will be miderstood by comparing the figure of the basioccipital 

 of the Iguana (PI. X. fig. 6) with that of the same bone in the Alli- 

 gator (fig. 7), in which, as in the Crocodiles and Gavials, the occipital 

 hypapophysis is a single, broad and thick process. 



I regret much the loss of the INISS. contaming the results of a very 

 careful study of the rich series of Mosasaurian fossils kindly submitted 

 to my examination by Prof. Rogers : they are alluded to by Sir H. 

 De la Beche in his 'Anniversary Address,' p. 27, where he quotes 

 one of the remarks relative to certain metacarpal or metatarsal and 

 phalangial bones, viz. that "they indicate the extremities of that 

 great Saurian to have been organized according to the type of the 

 existing Lacertia, and not of the Enaliosauria or marine lizards." 



I conclude this unavoidably brief account of the greeusand saurian 

 fossils by a notice of the very remarkable and well-defined form of 

 amphicaehan vertebra figured in PL XI. figs. 7 — 10. The subjects 

 of these figures are two vertebral centrums from the anterior part of 



