HTEACID^. 281 



species are distinguished by having a white dorsal spot. The type 

 specimen described by Mr. Fraser, and a young specimen received 

 from Sir Andrew Smith of his H. arboreus, are in the British 

 Museum. 



M. Blainville and other French zoologists have confounded the H. 

 dorsalis of West Africa with the H. arhorms of the Cape, which are 

 most distinct species, as proved by the types in the British Museum. 

 Dr. Peters described the H. arboreus as found on the coast of Mo- 

 zambique and also in the interior at Tete. 



The animals with the white dorsal spot have a very different skull 

 and teeth from the other species, which have a black or yellow dorsal 

 spot. Sir A. Smith observed the peculiarity of the teeth when he 

 described H. arboreus. 



The colour-spots on the back consist of the hair that covers the 

 situation of a dorsal gland on the vertebral line, about halfway 

 between the shoulders and the pelvis. 



In the species which have the hair yellow or white the streak is 

 generally narrow and linear ; in the species in which the spot is 

 black it is generally broad and diffased. In some specimens of H. 

 sinaiticus the yellow streak is deeper and brighter-coloured than m 

 others. It appears more marked in the younger and smaller speci- 

 mens in the British Museum than in the larger and older ones ; and 

 it is rather indistinct in the two skins which I believe may be IF. 

 ritficeps from Abyssinia. 



Professors Hemprich and Ehrenberg proposed to use the form of 

 the interparietal bone as a distinctive character for the species : thus 

 they described it as large and trigonal in S. eapensis, small and 

 pentagonal in H. syriacus, large and nesirly tetragonal in S. ruficeps, 

 and large and semiorbieular in H. Tiahessinicus. 



M. de Blainville, in the ' Osteographie,' " OnguHgrades," figures 

 the hinder part of the skull of three species to show the interparietal 

 bone ; he figures it as elongate and subtriangular in S. syriacus, 

 large, broad, and roundish four-sided ia H. eapensis, and very broad 

 in H. ruficeps. The part figured as the interparietal in the last 

 species is the broad upper edge of the occipital bone. 



Dr. Gr. V. Jaeger, who has several skulls from the Cape, collected 

 by Dr. Ludwig, and from North Africa by Dr. Heuglin, has written 

 an essay to show that the interparietal bone of the same species 

 varies much in form and size ; he figures ten varieties of it in IT. 

 eapensis and three in H. JMbessinieus. He seems to have confounded 

 two species under the latter name ; for fig. 14 is evidently a Dendro- 

 hyraoB, Dr. Jaeger having mistaken the broad upper edge of the 

 occipital bone for an interparietal : he also figures the interparietal 

 of a species sent from West Africa by Mr. Dieterle, which he names 

 H. sylvestris, which is also a Hendrohyraa: ; but the interparietal is 

 of a very different shape from those of the two skulls of the West- 

 African D. dorsalis in the British Museum. 



Dr. Jaeger shows that the interparietal is variable in shape in 

 Cavia aguii (Wiirzb. naturw. Jahresb. 1860, xvi. p. 158, t. 2). 



There is considerable difference in the form of the bladebone in 



