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Show 504 MR. O. THOMAS ON THE GENUS ECHINOPS. [June 14, None of the specimens show any trace of a lower m4. In these three genera of Centetidee and, so far as I can make out from the published figures, in Potamogale, we have a premolar formula of (0 2 3 4 ; the p4 (both milk and permanent) is abso- 1 2 3 4 lutely molariform, while p3 (again both milk and permanent) is functionally a " carnassial"-characters all in contrast to those of Sdlenodon, on whose close relationship to the Centetidee so much has been written. In this animal there are, it is true, three premolars as in Centetes and the others, but of these the first does not change, a fact which seems to show that it is homologous with the non-changing p1 of other Ferae, and not with the changing p2. If this be the case, and the two posterior changing premolars be still looked upon as p3 and p4, we get the formula P.j 1 0 3 4, while as a further difference \ 3 4 p3 is absolutely premolariform, and it is p4 that is functionally " carnassial" or semi-molariform, no premolar being truly molariform ; and finally there is neither that striking resemblance between the milk and permanent teeth, nor the unusually early development of the true molars, characteristic of the Centetidee. It appears to me therefore that not only was Dr. Dobson perfectly justified in separating the Solenodontidee as a distinct family from the Centetidee, with which Peters had placed them, but I would go further and suggest that their main connecting link- their common trituberculism-may be merely in each case a remnant of a time when, as the American zoologists have shown, trituberculism was a far more common character than at present, and that they have really no very close relationship to each other whatever. The proper solution of this problem will probably rest with the palaeontologists of North America, on which continent the ancestors of Solenodon may be expected to have lived ; and in consideration of its great general and geographical interest, I would specially commend it to the notice of any of them who may have the opportunity of examining remains referable to early Insectivora. The following is a tabular arrangement of the formulas above described, with the addition of that of Gymnura, put in for comparison with the rest. Numbers in italics represent teeth which, although present, are minute and apparently functionless. No definite suggestions as to the serial homologies of p1 or of the molars are intended to be conveyed by the type in which their respective numbers are printed. Centetes Ericulus. I. C. P. M. 1 2 0 1 0 2 3 4 1 2 34 1 2 3 1 2 3 4 1 2 3 1 2 3 4 1 2 3 1 0 2 3 4 123 120 1 0234 123 1 2 0 1 2 3 4 12 0 1 2 3 4 1 2 0 1 0 2 3 4 123 |
