612 PROF. W. H. FLOWER ON [Dec. 6, 



3. On the Pygmy Hippopotamus of Liberia, Hippopotamus 

 liberiensis (Morton) \ and its claims to distinct Generic 

 Rank. By W. H. Flower, C.B., LL.D., F.R.S. 



[Eeceived November 15, 1887.] 



The Zoological Department of the British Museum has lately 

 acquired a complete skeleton and skin of a fully adult Pygmy Hip- 

 popotamus. This animal has been separated generically from Hippo- 

 potamus by Leidy ^, under the name of Choeropsis ; and Leidy's view 

 has been adopted by Alphouse Milne-Edwards^ (who has given a very 

 careful description of the whole skeleton), by Gratiolet^, and by 

 others^ The two points of generic distinction insisted on are : — I. 

 The absence of the outer pair of lower incisors which are found in 

 Hippopotamus amphihius. II. The very different proportions and 

 relations of the parts of the cranium. 



It is admitted that in all other structural characters the two forms 

 are closely allied. 



I. With reference to the dentition, we may recall the division 

 which was made long ago by Dr. Falconer '^ of all the then known 

 species of Hippopotamus living and extinct into two subgenera, Hexa- 

 protodon and Tetraprotodon, according as they had three or two incisors 

 on each side of the jaw. The former term was afterwards raised 

 to generic rank by Owen^ , the old generic name Hippopotamus being 

 retained for Tetrnprotodon. Accepting this distinction as a valid one, 

 it was logical on the part of Leidy, on the discovery of a form with 

 only one incisor in the lower jaw, to separate it also generically. 



In his revision of the group, Mr. Lydekker does not accept these 

 divisions as generic, remarking that " the case of H. paJcdindicus, 

 which in its lower jaw is really a Hexuprotodon in process of conver- 

 sion into a Tetraprotodon, coupled with tlie instance of unilateral 

 hexaprotodontism in H. amphibius, indicates that Dr. Falconer's 

 two subgenera should be abolished. This point being admitted, there 

 are but slight grounds for retaining the subgenus or genus Choeropsis, 



^ Bippapofamiis minor, Morton, Proc. Acad. Nat. Sciences Philadelphia, 1844, 

 p. 14. Name withdrawn, as preoccupied, in favour of H. liberiensis, Morton, 

 Journ. Acad. Nat. Sc. Philad.2nd ser. vol i. p. 2.32 (1849). 



^ Chcerodes (Proc. Acad. Nat. Sc. Phil. vi. p. 52), withdrawn, as preoccupied, 

 in favour of Choeropsis (Journal Acad. Nat. Sc. Philad. 2ud ser. ii. p. 213, 

 1863). 



^ Kecherches pour servir a I'histoire naturelle des Mammiferes : Paris, 1868, 

 p. 77. 



* Eecherches sur I'Anatomie de THippopotame : Paris 1867. Apparently un- 

 aware of Leidy's generic name, Gratiolet proposed that of Bifomeodon (p. 202). 



' Macalister, " The Anatomy of Chxroiisis liberiensis," Proc. E. Irish Academy, 

 2nd ser. i. p. 494 (1873). The existing literature of this interesting species is 

 completed by reference to a description and figure of the sternum (which was 

 absent in ths skeleton described by Milne-Edwards) by Peters, Monatsbericht 

 Ak. Berlin, 1873, p. 445. 



^ Falconer and Cautlev, Asiatic Eesearches, xix. pt. i. p. 51 (1836). 



' Odontography, p. 566 (1840-45). 



