Berry — An Eocene Ancestor of the Zapodilla. 209 



(1753) and Sapota Miller (1759), the latter usage giving its 

 name to the family Sapotacese. Moreover Achras differs 

 from the fossil in the extent of its umbilical area. The genus 

 obviously has had a geological history, as yet unknown, and it 

 is quite possible that the umbilical character of the seeds may 

 have differed in the unknown fossil ancestors of the existing 

 form. At the same time it does not seem proper to amplify 

 what is one of the diagnostic characters of the recent genus to 

 include hypothetical fossil species. The fossil agrees with the 

 seeds of Calocarpum in the character of the umbilicus but is 

 smaller in size and more compressed. There are only two 

 known species of Calocarpum, one described as recently as 

 1914, and the other, known since 1762, has been placed 

 successively in the genera Achras (by Linne in 1762), Sideroxy- 

 lon (by Jacquin in 1762), Lucuma (by Gsertner in 1805), Vitel- 

 laria (by Radlkofer in 1882), Calospernum (by Pierre in 1890), 

 Achradelpha (by Cook in J 913), and still more recently (1914) 

 Pittier has taken up the generic name Calocarpum, first 

 proposed by Pierre in 1904. It will be seen that the paleobot- 

 anist can readily use a generic name for the present fossil seed 

 that will bring up either a different concept of the plant that 

 bore it in mind of each botanist according to his taxonomic 

 taste, or else no concept whatever. Moreover it is the acme of 

 improbability to suppose that the existing genera Achras, 

 Calocarpum, Lucuma, Vitellaria, Sideroxylon and Chryso- 

 phyllum were all fully differentiated as early as the middle 

 Eocene and that they have maintained their existing limits 

 since that time, an interval estimated by geologists as something 

 like three millions of years. Whatever credence the reader 

 may care to place in the latter estimate it is certain that the 

 fossil seed is older than the Pyrenees, the Swiss Alps 

 or the Himalayas. A further emphasis of the remoteness of 

 the fossil seed is furnished by the statement that the 

 contemporaneous tiny mountain horses (Orohippus), well 

 known from homotaxial deposits in the West, had live toes on 

 their fore feet and three toes on their hind feet. 



In view of the foregoing considerations I propose to 

 describe the fossil as the type of a new genus to be known 

 as Eoachras and I use this name in preference to Eocalocarpum 

 or Eolucuma because Achras has but one living species and 

 botanists are therefore in agreement regarding its characters 

 and affinities, and its name is not likely to change hereafter. 

 Moreover since this single living species may be regarded as 

 the type of the family, Eoachras may be considered to 

 represent the ancestral line that probably gave rise to more 

 than one of the modern genera enumerated above. The fossil 

 may be described as follows : — 



