XC11 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of Crustacea. Taking, however, into account all the objections to so 

 anomalous an interpretation, he next reversed his hypothesis, and 

 assumed " the quadrate disk to be the head, the hemispherical disk 

 to be the caudal extremity, and the exposed face to be ventral, — a 

 supposition which, though still not free from difficulty, exhibited, 

 on a comparison of the specimens with the Mysis or Opossum- 

 shrimp of our own sea, such curious points of resemblance as could not 

 be considered merely accidental ; and he therefore concludes that the 

 Pygocephalus Cooperi, which is the name he adopts, is probably more 

 nearly allied, notwithstanding an approximation in some respects to 

 the Squillidce, to the Mysis than to any other existing form, that it 

 is therefore a Podophthalmous Crustacean, and may safely be assigned 

 a place among either the lower Decapoda or the Stomapoda, affording 

 the first certain evidence of the existence of Podophthalmia at so 

 early a period as the Carboniferous epoch. 



In another paper, Professor Huxley described a new species of 

 Plesiosaurus, procured at Street, near Glastonbury, and now in the 

 Museum of Practical Geology, Jermyn-street. As this species will 

 be described at length in the Decades of the Geological Survey, the 

 object of Professor Huxley was principally to point out the peculiar- 

 ities of the atlas and axis, and of the cranium of that genus. The 

 species resembles most P. Hawhinsii, and is about the same size, 

 being between seven and eight feet long ; but it has 53 cervico-dorsal 

 vertebrae, of which 30 are cervical, whilst in P. Hawhinsii there are 

 31 cervical, and at least 23 dorsal. The species is therefore charac- 

 terized as having 53 cervico-dorsal vertebrae, by a cranium not more 

 than y^th of the length of the body, the 30 anterior vertebrae being 

 fully, or more than, four times the length of the cranium. It has 

 been named P. Etheridgii. The atlas and axis are (as stated by 

 Professor Owen to be characteristic of the genus) anchylosed ; but 

 their structure is very different from that exhibited in the genus 

 Ichthyosaurus, and more nearly resembles the corresponding parts of 

 the Crocodile. 



Professor Huxley then pointed out the many points of structural 

 correspondence between Plesiosaurus and Teleosaurus, and questions 

 the accuracy of the very backward position of the posterior nares 

 ascribed to Plesiosaurus, which would be in opposition to such an 

 analogy, as the posterior nares in Teleosaurus are far more forward 

 than in Gavialis, and in the Gavial more forward than in the Cro- 

 codile. He thinks it therefore more probable that the so-called 

 posterior nares of Plesiosaurus correspond with the deep fossae on 

 cither side of a prominent median ridge visible on the under surface 

 of the basi-sphenoid of Teleosaurus. Some other structural analogies 

 between Teleosaurus and Plesiosaurus were noticed ; and Professor 

 Huxley stated that in many respects the Teleosaurus appeared to 

 afford a link, before not noticed, between the long-necked Enalio- 

 saurus and the existing Crocodile, a conclusion in the interest of 

 which, when the relations of time are considered, the genus Plesio- 

 saurus must manifestly share. 



In respect to the ancient flora, Mr. Salter has submitted a notice 



