ARTHROPOD A— INSECTA. 443 



According to this author, the total number of known Tertiary 

 and Quaternary species of insects (including all four classes) is 

 something over 5,800, while the number of known recent species 

 is over 384,000. In the following synopsis of the orders repre- 

 sented in the American Tertiary and Quaternary deposits, the 

 diagnoses as given by Handlirsch are closely followed. 



THYSANURA Latr. 



{Apt era, Spring tails. ) 



Order LEPISMOIDEA Handlirsch. 



Small wingless insects developing without metamorphosis ; head 

 with broad basis joined to thorax, which consists of three divisions; 

 tergite not well developed, pleurite and sternite strongly so; pro- 

 thorax as large as, or larger than, mesothorax; legs ambulatory, 

 not modified for springing; abdomen of ii segments and a telson. 

 The only American species is Lepisma platymera Scudder, from 

 the Oligocenic "lake beds" of Florissant, Col. 



PTERYGOGENEA Brauer. 



Order ORTHOPTERA (Oliv.) Handl. 



(Grasshoppers, locusts, crickets, etc.) 



With coriaceous fore wings and delicately veined thinner hind 

 wings; the five principal veins of the wings with all their furca- 

 tions extending to the outer margin of the wing. Anal area large 

 in hind wings, often small in front wings and modified in the male 

 locust into musical organs ; C of front wings separated from an- 

 terior margins, Sc and R simple, the Sc as well as the C may have 

 forward directed branches; Rs with oblique backward directed 

 branches; M simple or branched, abundantly so in fore wings of 

 Acridioidea; Cu often much reduced ; anal veins generally branched 

 or fan-shaped; cross-veins abundant. Of the 75 known Tertiary 

 and Quaternary species, 17 are American, 10 from Florissant, Col. 

 (Oligocenic), 6 from the Green River beds of Wyoming (Eo- 

 cenic), and i from the Eocenic of Greenland. The number of 

 recent species is about 6,300. 



American Tertiary locusts {Locustidce) are known from Floris- 



