116 THE UNIVERSITY SCIENCE BULLETIN. 



KEY TO RHEUM ATOBATES. 



Taken from Bueno's Gerrids of Atlantic States.* 



A. Hind femora and coxae of male curiously swollen and distorted. 

 Female with mesosternum unicolorous. R. rileyi Bergr. 



AA. Hind femora and coxae of male not swollen and distorted. Female 

 with mesosternum yellow with the anterior margin and the two 

 posterior diverging bands brownish-black, these bands not reaching 

 to the posterior margin and dilated near the anterior margin. 



R. tenuipes Meinert. 



Genus HALOBATES Eschs. 



"Head triangular; eyes, globular; beak, short and stout. Fourth seg- 

 ment of antennae longer than the third. Mesothorax very large; abdo- 

 men, short and conical; front legs, short and femora thickened some- 

 what. Middle legs, very long and slender. The hind legs shorter than 

 the middle ones. Found upon the floating mats of seaweed often far at 

 sea. The two species reported from our land were described by Esch- 

 scholtz in 1822. The descriptions here given are from Burmeister's 

 Handbuch." 



Halobates sericeus Eschs. 



Eschscholtz, Entomographien, p. 108, 1822; Burmeister, Handb. d. Ent. II, p. 209, 1835. 



"Corpore ovali, subtus argenteo, supra albo-cinereo; oculis flavis. 

 Long., IVs'"." 



Locality: Florida. 



Halobates micans Eschs. 



Eschscholtz, Entomographien, p. 107, 1822; Burmeister, Handb. d. Ent. II, p. 208, 1835. 



"Corpore conico, subtus argenteo, supra cinereo, seneo, miconte; oculis 

 atris. Long., 1%'"." 



Locality- California. 



B. Biology of the Gerrids. 



General Notes. The water striders are to be noted everywhere. 

 Bueno says "their haunts range from living springs, clear, secluded, 

 shady, and cool, to the vast expanse of the tropic ocean steaming under a 

 torrid sun, or dashed by wild storms into mighty waves." So far as we 

 know them, the fresh water forms place their elongate white eggs upon 

 supports at the water's surface. They feed upon organisms nurtured in 

 the water, or upon plants about the shore. They also prey upon flounder- 

 ing insects that chance to tumble into the water. Bueno and Drake have 

 given us life history notes upon the group and Essenberg has studied the 

 behavior of some of them. 



Genus GERRIS Fabr. 



For this country we have life history notes by Bueno upon G. mar- 

 ginatus and G. remigis, and by Drake upon G. conformis. The writer has 

 studied the first two in Kansas. 



Gerris remigis Say. 



Habitat. This large strider is usually apterous and more often found 

 on running water, or pools connected therewith, than on isolated small 

 ponds. They are gregarious fellows, seeking a resting place in the shade 

 of overhanging bank or bush, but taking wildly to the open when alarmed. 



* A third species R. trvlUger, Bergr. is described in Bui. Brookl. Ent. Soc. X, p. 63, 

 1915. Mv manuscript for this genus has been misplaced. Bergroth has a splendid paper 

 in Ohio Naturalist, vol. VIII, p. 381. 



