fi76 l''AMILY XXXIII. PARNIDJE. 



aquatic plants. They feed upon decomposing matter in the water 

 and thus form one of the agencies which nature has provided for 

 purifying streams. The legs ar(^ not fitted for s^^dmming, but the 

 fifth or last .joint of the tarsi is longer than the other four united, 

 and is armed with long, simple, claws, whence the common name 

 above given. This structure of the tarsus is the principal distin- 

 guishing character of the family and enables its members to grasp 

 firmly objects resting in strong currents of water. By taking an 

 old limb or rough stone from the water at a suitable locality and 

 placing it in the sun, the insects will move as the water dries, 

 though at first nothing can be seen of them, so perfectly do they 

 resemble the surface on which they rest. The surface of the body is 

 clothed with fine silken hairs which have the property of repelling 

 or shedding water and enable the insect to surround itself with a 

 film or globule of air while dinging to objects beneath the water. 



The larva of our largest species, Psephenus leeontei, resembles in 

 appearance a trilobite, being flat and nearly circular in outline, and 

 measuring about 8 mm. in length. It is found clinging to stones in 

 rapid water or in muck near springs or ponds. The larvse of the 

 genera Elmis and Stenelmis are said to be similar in form, except 

 that the segments are not united to the margin, which thus appears 

 notched or incised. 



Among the more distinctive characters of the family are the 

 usually retractile head, with distinct labrum and small mandibles ; 

 prosternum distinct in front of the coxaj, usually elongate behind 

 and forming a process received into a definite cavity in the meso- 

 sternum ; front coxal cavities widely open ; hind coxa3 transverse and 

 usually dilated into a plate, which partly protects the thighs; elytra 

 entire; alidomen usually with five venti'al segments, the front ones 

 connate or firmly united. 



Nearly 400 species of the family are knowTi, about 50 of which 

 occnr in North America. The principal literature treating of these 

 is as follows: 



Lrr-on/c— "Synopsis of the Parnida^ of the United States," in 



Proc. Phil. Acad. Nat. Sci.. VI, 1852, 41-44. 

 /7rtr)i,.—" Synopsis of the Parnidaa of the United States," in 



Trans. Amer. Ent. Soc, III, 1870, 29-42. 



The North American species are distributed among three sub- 

 families, all of which are represented in Indiana. 



