252 PROF. FLOWER ON HYDROCHffiRUS CAPVBARA. [Ma)' 6, 



The species of Reptiles recognized as hitherto known to occur in 

 the Solomon Islands were stated to be 19, and those of Batrachians 

 9 in number. 



This paper will be published in the Society's ' Transactions.' 



The following papers were read; 



1. Note on the Dentition of a young Capybara (Hydrochwrus 

 capybara) . By Professor W. H. Flower, L.L.D., F.R.S., 

 P.Z.S., &c. 



[Eeceived April 7, 1884.] 



As is well known, the incisors of the simplicident Rodents have 

 no milk predecessors. With regard to the molars, the rule seems to 

 be the following. When there are only three (as in the Common 

 Rat), or fewer than three (as in Hydromys), these are all true 

 molars, and have no predecessors. These animals then are truly 

 monophyodont. When the number exceeds three, it is by the 

 addition of teeth to the front of the series, which are premolars and 

 are preceded by milk-teeth. In the large majority there is only 

 one such tooth on each side. 



When milk-teeth are present, a remarkable variation is observed in 

 their characters and the period at which they are matured and shed. 

 Thus in the Guinea-pig and its allies the one milk-molar (a small, 

 though tolerably well-formed tooth) is absorbed or shed a short 

 time before birth ; while in the Porcupines and Beavers the cor- 

 responding tooth is retained until the animal has nearly reached the 

 adult condition l . 



On Nov. 30, 1875, two Capybaras were born in the Society's 

 Gardens : one died on the same day, the other lived until the 8th of 

 December. The skull of this one was preserved, and is now in the 

 Museum of the Royal College of Surgeons. It show's the state of 

 dentition at this early age particularly well. 



In the adult Capybara the dental formula is ?'. *, c. °, p. ~, m. | = 20 ; 

 the distinction between premolars and molars being inferred from 

 the analogy of other Rodents, in fact of other placental Mammals. 

 In the little animal eight days old, the cranium of which measures 

 102 millim. in length, the number of the teeth is just the same as 

 in the adult ; the incisors and four molariform teeth being all 

 present and in an ecpaal state of development. A small portion of 

 the surface of each, including the posterior molar, has been already 

 abraded by wear. The molar teeth show the same form and pattern 

 as in the adult, being each divided by deep lateral grooves into 

 distinct lobes corresponding to those of the full-grown tooth. They 

 are, however, all very much smaller, the length of the whole series 



1 See " Notes on the First or Milk Dentition of the Mammalia," by W. H. 

 Flower, Transactions of the Odontological Society of Great Britain, iii. 1871 

 pp. 211-232. 



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