1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 51 



Berosus striatus Say 



The stages of this species are very close in form to those of B. pere- 

 grinus and a separate description is unnecessary. The left mandible of 

 the larva is quite similar to that of peregrin us but the right one has only 

 the distal inner tooth well developed. The other two teeth are very 

 rudimentary. As both the species belong to the same subgenus, Berosus, 

 this character evidently is not one of subgeneric significance. Larvae 

 in the National Museum of B. cericeps (= signaticollis Charp.), which 

 belongs to the same subgenus, possess the peregrinus type of mandible 

 but have the labro-clypeus untoothed, rounded and short. The labro- 

 clypeus of B. striatus is similar to peregrinus but the number of teeth 

 varies from three to six. 



CHiETARTHRiA Stephens 



Four species have been described from this country. C. atra LeConte, 

 1883, however, is the local species near Cayuga Lake and is very rare. 

 In the field it could easily be mistaken for Anccena and Paracymus but is 

 usually smaller and noticeably hemispherical in shape. Closer examina- 

 tion clearly distinguishes it. The first segment of the antennae is elon- 

 gate and flattened. The ventral plates, fringed with appressed setae and 

 concealing the first two abdominal sternites, constitute the most striking 

 characters of this genus. 



The life history has not been observed. The structure of the 

 abdomen possibly indicates that the egg-cases may be held on the 

 ventral side of the female, somewhat in the same manner as in Epime- 

 topus. 



Hydrobius Leach 



One experiences little difficulty in separating H. fuscipes and H. 

 globosus, the two species which are present in the Cayuga Lake basin. 

 As the name globosus suggests, this member is strikingly globular in form, 

 while fuscipes is much flatter and more elongate. Both are almost 

 entirely black in color but the reddish brown legs of fuscipes are char- 

 acteristic of that species. They are not very often taken together, al- 

 though they have been recorded from similar habitats. H. globosus 

 seems to prefer the banks of rapidly flowing streams or spring-fed pools, 

 filled with leaves or vegetation, while fuscipes abounds more often in 

 stagnant waters. However, where the leaf-filled pools tend to become 

 stagnant both species usually occur. 



