Prof. Huxley on a New Species 0/ Plesiosaurus. 321 



By a happy accident the only displacement in the whole length of 

 the vertebral column of this specimen has taken place between the 

 head and the atlas and axis, on the one hand, and between the 

 latter and the third cervical vertebra on the other. By a little 

 careful clearing away of the surrounding parts, it has thus been 

 possible to expose the atlas and axis very easily. They are, as 

 Prof. Owen has stated to be their character in this genus, anchy- 

 losed ; but their structure is totally different from what is seen in the 

 Ichthyosaurus, and closely resembles that of the corresponding parts 

 in the Crocodile. An os odontoideum, very similar to that in the 

 Crocodile, represents, as Rathke long since demonstrated in other 

 Reptilia, the central portion of the body of the atlas ; while its 

 cortical inferior portion and its neural arches form an anterior arti- 

 cular cup for the occipital condyle, as in the Crocodile. 



The author next adverts to the many points of structural corre- 

 spondence observable between Plesiosaurus and Teleosaurus, not only 

 as regards the atlas and axis, but as respects the cranium. 



The existence of a distinct jugal and squamosal, and of a union 

 between the latter and the post-frontal, and the consequent sub- 

 division of the temporal fossa, as in the Crocodile, are indicated. 

 The extension of the exoccipitals and of the pterygoids to the 

 OS quadratum is adverted to ; and the very backward position of the 

 posterior nares ascribed to Plesiosaurus is questioned. Teleologi- 

 cally, such an arrangement appears not very comprehensible : and, 

 on morphological grounds, it is unlikely ; for the posterior nares are 

 more forward on the base of the skull in Gavialis than in Crocodilus, 

 and far more forward in Teleosaurus than in Gavialis. It seems more 

 probable that the so-called posterior nares of P/e5«oso!wrM5 correspond 

 with the deep fossae on either side of a prominent median ridge 

 visible on the under surface of the basi sphenoid of Teleosaurus. 



The petrosal bone, completely covered externally by the qua- 

 dratum in Crocodilus, is partially exposed in Gavialis, and com- 

 pletely so in Teleosaurus and in Plesiosaurus. 



Similar comparisons were pursued with respect to other parts ; 

 and it is shown that in many respects the Teleosauria bridge over the 

 gap between the long-necked Enaliosauria and the existing Croco- 

 dilia, — a conclusion not without interest, when the relations in time 

 of the two orders are consideied. 



3, " On the Coal found south of Concepcion, in Southern Chdi." 

 By Dr, C. Forbes, R.N. (In a letter to the President.) 



The coal is found in seams alternating with shales and overlaid by 

 calcareous sandstone ; fire-clay underlies the whole. The shales con- 

 tain fine impressions of dicotyledonous leaves ; and some of the sand- 

 stones above the coal abound with casts of a Mactra-like bivalve ; and 

 others with Turritellse. From this association of fossils. Dr. C. Forbes 

 believes that tiie coal is decidedly not of paheozoic age, and may 

 be tertiary. 



4. " On a quantity of Crabs thrown up on the beach in Payta 

 Bay," By Dr. C. Forbes, R.N. (In a letter to Prof. Ansted, F.G.S.) 



Phil. May. S. 1.. Vol. 15. No. 100. April 185.S. Y 



