Dr. Grant on Mastodontoid Animals. 465 



For the determination of the dental formula; of Mastodon and Te- 

 tracaulodon, Dr. Grant relied entirely on the splendid collection of 

 jaws, crania, and teeth in Mr. Koch's possession, which afford ample 

 means for the solution of that problem. For the dental formula of 

 Deinotherium he has been indebted solely to the casts and fragments 

 of that genus in the British Museum. After explaining the uncer- 

 tainties and fallacies to which naturalists have been exposed in the 

 identification of species, from not having ascertained the entire dental 

 series in any Mastodon, the sixth section of the memoir describes the 

 distinctive characters and the distribution of the Mastodon angusti- 

 dens, M. latidens, M. Elephantoides, M. minutum, M. Tapiroides, M. 

 Andium, M. Borsoni, M. Humboldtii, M. Turicense, M. Avernense, 

 M. giganteum, M. Cuvieri, and M. Jeffersoni. The seventh section 

 of the memoir is devoted to the examination and description of the 

 generic characters of Tetracaulodon, as established by Dr. Godman, 

 and as founded on the number and form of the teeth, the peculiarities 

 of their microscopic structure, the form of the jaws, the tusks, the 

 alveoli of the tusks, the intermaxillary fossa, the infra-orbitary fora- 

 mina, and other influential characters. The eighth and last section 

 of this paper is occupied with an account of the distinctive characters 

 and the distribution of the known species of this genus ; viz. Tetra- 

 caulodon Godmani, T. Collinsii, T. Tapiroides, T. Kochii, T. Haysii, 

 and T. Bucklandi. 



June 29, 1842. — Seven communications were read. 



1 . " Notices connected with the Geology of the Island of Rhodes." 

 By Mr. T.A.B. Spratt, Assistant-Surveyor of H.M.S. Beacon. Com- 

 municated by C. Stokes, Esq., F.G.S. 



The observations detailed in this paper were made during the sum- 

 mer of 1 840. The geological structure of the Island of Rhodes, Mr. 

 Spratt states, is simple, and the distribution of the deposits easily 

 defined. The formations consist of mica schist, shales, limestones, 

 trachyte with basaltic rocks, large beds of shingle, both anterior and 

 posterior in origin to the volcanic aera $ and very extensive tertiary 

 deposits. 



The mica schists occur in the central districts near Alleyermah and 

 Sclipio, but do not form ridges of very great altitude. 



The limestones are scattered in detached masses and rest appa- 

 rently on argillaceous shales of a black, light cream or reddish colour, 

 but the positive order of superposition the author had np opportunity 

 of determining. He failed also in detecting in them any organic re- 

 mains, but he is of opinion that they are of contemporaneous origin 

 with the strata near Smyrna, assigned by Mr. Strickland to the Hip- 

 purite limestone. The shales are well developed in several places 

 around the base of Mount Ottayaro, but more particularly in the 

 valley west of the village of Embono. 



Both the schists and the limestones exhibit, Mr. Spratt states, 

 proofs of great dislocations, and he is inclined to ascribe these effects 

 to the outburst of the volcanic rocks which constitute^so large a por- 

 tion of the central and southern districts of the island. He mentions 

 as instances of these disturbed beds a thin stratum of limestone which 



Phil. Mag. S. 3. Vol. 23. No. 154. Dec. 1843. 2 H 



