1899.] ON THE PLEXODOKT MOLARS OE MAHMaLS. 555 



fringes 15. The left opercular gill ^vas absent, and nothing indi- 

 cated its absence to be the result of an injury. 



Mr. E,. Lydekker, F.Z.S., exhibited a pale-coloured specimen of 

 the Eeed-buck (Cervicapra arundinum), and read the following 

 notes on it, extracted from a letter addressed to him by Mr. Ewart 

 S. Grrogan : — • 



"I have much pleasure in forwarding to you the horns, head-skin, 

 and hide of what appears to be a white Reed-buck. I shot the latter 

 on the Longwe, at the north end of Lake Nyasa. Capt. Verhellen, 

 of Mohun's expedition, first called my attention to it, by asking me 

 (he knows nothing of the game in this part) what those little grey 

 antelope were ; he was veri/ positive as to having seen four : one, a 

 female, he wounded and lost ; but though I hunted the small plain 

 where he states he saw them, I never found any but the ram I killed, 

 and it is the Eeed-buck's habit to generally run in the same party ; 

 i. e. four running together would, I think, never go far apart, at 

 any rate at the same season of the year. The natives whom I 

 questioned closely say they have seen one only ; but this counts 

 for little. The buck showed no signs of albinism — lips, nostrils, 

 eyes, and hoofs being of the normal colour. On comparing the 

 skull with two others I thought I detected considerable variations, 

 especially in the base of the skull. Will you kindly describe the 

 animal for me, and bring it before the notice of those who are 

 interested in this branch of zoology ? Personally I am inclined, 

 owing to the persistent rumours of similar animals in this country, 

 the striking aud very definite assertion of Capt. Verhellen, and tlie 

 complete absence of the usual signs of albinism, to think that it 

 is a distinct form. I have taken what measures I could to preserve 

 the skin and trust that it will arrive in good order." 



The following papers were read : — 



1. On the Primitive Type of the Plexodont Molars of 

 Mammals. By Florkntio Ameghinoj C.M.Z.S. 



[Received February 13, 1899.] 



The majority of placental Mammals, and especially the Ungulates, 

 are distinguished by the plexodont character of their molars — that 

 is, by molars having a complicated crown, and each tooth being 

 provided with more than one root. 



The origin of this dentition has been explained by two completely 

 different theories — the theory of a gradual complication, and that 

 of fusion. According to the former, the plexodont molars are the 

 result of a progressive complication of the simple and conical 

 primitive tooth of Eeptiha. According to the latter, these same 

 teeth are the result of fusion of the dental germs or embryos of 



