46 



It may well be doubted if, in most cases, species of Celtis can 

 be distinguished by means of the characters of the stones. This 

 can be done in the case of some of the existing species, but is 

 impossible in the case of others. The present species of Celtis 

 is associated with a leguminous seed which it has not yet been 

 possible to identify. 



The genus Celtis is a most interesting member of the family 

 Ulmaceae, in fact the whole family bristles with problems of 

 distribution and geologic history, and none of the genera surpass 

 Celtis in this respect. As currently understood Celtis includes 

 about eighteen fossil species ranging in age from Eocene to 

 Pleistocene. The Eocene species are four in number and all are 

 American. The Oligocene species are also four in number and 

 are North American and south European. The rather numerous 

 Miocene species are found in Europe and in North and South 

 America. The Pliocene species are European and Asiatic. The 

 Pleistocene species known to date are all North American and 

 represent the section Euceltis of Planchon. 



The living species of Celtis number about 90 and are widely 

 distributed and usually divided into four sections or sub-genera, 

 namely: Euceltis, Sponioceltis, Solenostigma, and Momisia, 

 which are sometimes considered and are probably entitled to 

 generic rank. The present fossil species belongs to the sub-genus 

 Momisia' of Dumortier, which has about 25 existing species 

 ranging from Texas to the Argentine, and with the genera Am- 

 pelocera, Trema, being especially characteristic of the warmer 

 parts of South America. Momisia appears to have invaded the 

 southern United States from equatorial America along with the 

 fossil flora that characterizes the middle and upper Eocene in 

 that region. 



In view of the impossibility of making fine discriminations 

 from the fruits alone, the present fossil species is referred to 

 Celtis, using that term in the wider sense. The majority of the 

 existing species are mesophytic types of humid regions, but 

 several of the forms, notably Cekis occidentalis Linn., in our 

 western states, and Cellis iala in the northern Argentine, survive 

 very adverse conditions and aridity. 



Johns Hopkins University, 

 Baltimore, Md. 



