I9I4.] SOUTHEASTERN NORTH AMERICA. 229 



While future discoveries will have to greatly amplify the fossil 

 record before the history of the family in past times can be traced 

 with any degree of surety, the remarkable display of these forms 

 in the Mississippi embayment region, evidently derived from the 

 American tropics, gives a large amount of probability to the theory 

 that the family originated in the American tropics during the 

 Upper Cretaceous. 



The genus Trapa Linne, formerly included in the family Ono- 

 graceae, is now made the type and only genus of the family Hydro- 

 caryace?e (Trapace^e, Dumort, 1827). There are three existing 

 species, all aquatics, and all confined to the old world except for 

 the naturalization of Trapa iiatans Linne, in New England and 

 New York. The latter species is found irregularly scattered through- 

 out central and southern Europe, its area of distribution being a 

 contracting one as shown by its occurrence in post-glacial deposits 

 at very many localities beyond its present range in Russia, Finland, 

 Sweden and Denmark. The two other existing species are Trapa 

 bicornis Linne of China and Trapa bispinosa Roxburg of south- 

 eastern and southern Asia (said also to occur in xA.frica). 



The genus has an extended geological history. Rosettes supposed 

 to represent the floating leaves (Trapa ? micro phylla Lesq., and 

 Trapa ? cuneata Knowlt.) are widespread in the Rocky Mountain 

 province in beds of late Cretaceous and early Tertiary age. The oldest 

 recognizable fruits are a large bi-cornute form from the Eocene of 

 Canada and Alaska and Trapa wilco.vciisis Berry found in the Wil- 

 cox flora. An Oligocene species ( Trapa Crcdncri ) Schenk has 

 been described from Saxony, and no less than seven species have 

 been described from the Miocene — two occurring in Idaho (Payette 

 formation), one in Japan and the balance in Europe, where two 

 species continue into the Pliocene. A species from the late Pliocene 

 of America is found in southern Alabama. The existing Trapa 

 nataiis has been recorded from the preglacial beds of England and 

 Saxony and from very many interglacial and postglacial deposits in 

 Portugal, Italy, Netherlands, Germany, Sweden, Russia and Den- 

 mark, Gunnar Andersson in a recent paper (1910) mentioning 18 

 localities in \Vest Prussia, 6 in Denmark, 17 in Sweden and 29 in 

 Finland. 



