THYSAXURA. 6 1 



EE. Head more or less concealed under the thorax. Lepidocyrtus. 

 BB. Without scales. 



C. Abdominal segments unequal. Entomobrva. 



CC. Abdominal segments subequal. Isotoma. 



Family IV. PODURID^E. — The Poduridce comprises two genera, 

 Achoriitcs, in which the tarsi have two claws, and Podura, in which 

 there is but a single claw on each tarsus. Certain species of each 

 genus are found on the surface of standing water. Our common 

 " Snow-flea" is AcJiorutcs nivicola. This is sometimes a pest where 

 maple-sugar is made ; the insects collecting in large quantities in 

 the sap. 



Family V. LlPURID^E. — The body is cylindrical in form ; there 

 is no saltatorial appendage ; and the mouth-parts are formed for 

 biting. Only a single genus, Lipura, has been described. 



Family VI. AnOURID^E. — This family resembles the preceding 

 in the cylindrical form of the body, and in the absence of a saltato- 

 rial appendage ; but it differs from all other members of the Thysa- 

 nura, in having the mouth-parts formed for sucking. The mouth- 

 parts are exceedingly rudimentary; there being neither mandibles nor 

 maxillae. There is but a single genus, Anoura, known. The name 

 of this genus will doubtless be changed, as it is preoccupied by a 

 cenus of bats. 



