124 TERTIARY INSECTS OP NORTH AMERICA. 



Length of body, 9.5 mm ; width of head, 1.3 mm ; of thorax, 2"; length of 

 femora, 1.2 mm ; of wing pad, 2""; of sette, 2.5 mm . 



Florissant. Two specimens, Nos. 1.582, obtained by the Princeton ex- 

 pedition, and 1070G. 



EPHEMERA EXSUCCA. 

 PI. 12, Fig. 9. 



A single specimen, very badly preserved, but showing unmistakably 

 the caudal seta?. The whole is preserved as I have seen no other specimen 

 from Florissant, as if drawn on the stone with a pale blue pencil. The 

 body is tolerably stout for an Ephemera, the abdomen tapering a little. The 

 expanded wings are only partially preserved, but are apparently nearly as 

 long as the body. The three caudal seta; are very slender and of exactly 

 the same length, a little shorter than the body. No ciliation can be detected 

 on them. 



Length of body, 9 mm ; breadth of thorax, 2 mm ; expanse of wings, 16"""; 

 length of caudal setse, 7 mm . 



Florissant. One specimen, No. 5587. * 



Family ODONATA Fabricius. 



More than thirty years ago in his work in conjunction with de Selys 

 on the European Odonata, Dr. Hagen contributed a chapter on the fossil 

 species of Europe, in which about half of the species enumerated (thirty- 

 nine in number) belonged to the Secondary and half to the Tertiary period. 

 Since then no one has done more than Dr. Hagen to add to our knowledge, 

 especially of the Secondary species. The time has hardly come, and the 

 species known are as yet perhaps not sufficiently numerous, to enter on any 

 study of the relation of the Secondary and Tertiary types ; but it may be 

 stated in a general way that, omitting all mention of larval remains, we 

 now know nearly double the number then recorded, and the Tertiary 

 species are considerably in excess. Of these the larger part belong to the 

 Agrionina. (January, 1882.) 



To enter into a few details, the strongly limited group of dragon-flies 

 makes its appearance in the Lias in considerable variety and apparently as 

 highly specialized as to-day, for no less than four tribes are present, the 

 true Agrionidae and the Cordulidre alone being absent. Aeschnina are the 



