236 DR. MORTON'S OBSERVATIONS ON 



Hippopotamus comprises two subgenera, Hexaprgtodox, with six incisors above 

 and below ; and Tetraprotodon, the species with reduced incisors, viz., four above 

 and below. Your species, although it has but two in the lower jaw, belongs to the 

 latter subgenus. The excessive reduction is probably only an individual case of 

 variety, but if proved to be constant, the position of species in the genus will not be 

 altered. The succession of the species in the table indicates the order of their 

 affinities. No. 1, H. majoVjis the most divergent form, with short cranium, posterior 

 orbits, great elevation of the sagittal and occipital crests, and excessive elevation of 

 the upper margin of the orbits above the plane of the brow. Next follows H. 

 palceindicus, (No. 2,) a true fossil Hippopotamus from India. Then comes 

 H. amphihius, No. 3 in the series, of which the French naturalists make two species, 

 Capensis and Senegalensis. 



Duvernay, in a late memoir, (Comptes Rendus, October 1846,) maintains their 

 distinctness, but I regard them as merely varieties. H. annecteus, No. 4, is an 

 undescribed fossil species from the Nile above the Cataracts, which I lately observed 

 in the Frankfort collections, (the Senckenberg Museum,) and brought to Europe by 

 Dr. Riippel in 1827. I have named it H. annecteus from its forming a link in size 

 between H. amphibius and your species. The cranium is not known. Cuvier's 

 H. medius has proved to be a species of Dugong, {Halitherium of authors.) Next 

 follows Cuvier's H. minor, No. 5, which is a doubtful Tetraprotodon. I range your 

 species last, from its close resemblance to the Indian Hezaprotodons in the form of 

 the upper canines, No. 6. 



Of Hexaprotodon, we have three well-marked Indian fossil species. H. Iravaticus, 

 No. 7, is a size larger than your li. Liberiensis. H. sivalensis, No. 8, is less than 

 H. amphibius ; and B.. namadicus, No. 9, with other strongly marked characters, is 

 laro-er than H. amphibius, or the H. sivalensis. We possess portions of every part of 

 the skeleton, showing the closest resemblance to Hippopotamus amphibius throughout, 

 but more slender in the proportions. Merycopotamus is a most interesting and well 

 marked genus, connecting Hippopotamus with Anthracotherium. The molar teeth, 

 as in the latter, are constructed on the ruminant plan ; while the cranium, incisors 

 and canines, together with the leafy expansion of the angle of the lower jaw, connect 

 it with the former. It was nearly of the size of your H. Liberiensis. 



SYNOPSIS OF THE HIPPOPOTAMIDiE, FOSSIL AND EEC E NT. 

 Genus 1. HIPPOPOTAMUS. 



Subgenus 1. Tetraprotodon. 



1. H. (Tet.) major. Europe. Fossil, 



2. H. (Tet.) pal^indicus. India. Fossil. 



