464 Geological Society. 



2. Tellina Groenlandica, which is found abundantly at St. Henry, 

 and to a less extent on Logan's Farm and on " the Mountain." 



3. Tellina calcaria. — One valve of this shell was picked up on 

 ** the Mountain." 



4. Mya truncata. — Several hinges of this species were obtained at 

 St. Henry. 



5. Mytilus. — A broken valve was found on " the Mountain." 

 The first four fossils, Mr. Logan says, he has been informed, were 



found by Mr. Murchison and M. de Verneuil at Ust Vaga, 250 miles 

 from the White Sea, and 130 feet above its level. He also alludes 

 to Mr. Lyell's comparison of the Quebec shells with species which 

 occur at Uddevalla. 



A communication was afterwards made by Dr. Grant, F.G.S., 

 " On the Structure and History of the Mastodontoid Animals of 

 North America." 



The chief object of this communication was to point out the 

 structural differences and zoological distinctions of the Mastodons 

 and Tetracaulodons of North America ; and the inquiries were in- 

 stituted in consequence of the favourable opportunity afforded by the 

 temporary exhibition, in this metropolis, of Mr. Koch's barge collec- 

 tion of organic remains from the State of Missouri, consisting prin- 

 cipally of the relics of these two genera. 



After pointing out the important applications of the study of these 

 remains, and the geological relations of Mastodontoid animals, and 

 the discordant opinions of zoologists as to their specific distinctions, 

 Dr. Grant entered into extended details regarding the general struc- 

 ture and the peculiarities of the skeleton in the three principal 

 Mastodontoid genera, Mastodon, Tetracaulodon, and Deinotherium, 

 which are compared with those of the elephant and other allied ge- 

 nera. The fifth section of the memoir is occupied with the descrip- 

 tion of the development, forms, structure and changes of the dental 

 system of Mastodontoid animals ; and each tooth and tusk of the 

 three principal genera are described and compared, and the principal 

 modifications they exhibit according to difference of age, sex, and 

 species. After pointing out the necessity of including the entire se- 

 ries of successive teeth, in the dental formula? of genera, where the 

 teeth are constantly displacing and succeeding each other through 

 the whole of life, the author announces the dental formulae of the 

 four Proboscidian genera of Pachyderma to be 



2 8—8 

 Elephas,Inc. -jr-, can. -^-, mol. -, = 34. 



Mastodon. Inc. -pr, can. -z~. mol. = ~, = 26. 



' o—o 



, JT 2 ° ,6-6 



Tetracaulodon, Inc. -77, can. -jr. mol. s ~, = 28. 



2 6 — 6 



x. . , • ,, ,5-5 



Deinotherium, Inc. _ , can. „ , mol. . _ ^ -, = 22. 



