COLEOPTERA 481 



The most common of all ground-beetles, in the Northeastern States 

 at least, is Poecilus lucubldndns. In this species (Fig. 1 64) the nar- 

 row, flat margin on each side of the prothorax is widened near the 

 hind angle of this segment. 



The family AMPHIZOID,^ is represented in our fauna by two 

 species of Amphizoa, which occur in California, Vancouver, and 

 Alaska, clinging to logs or stones under the surface of streams. In 

 these beetles the metastemum is truncate behind, not reaching the 

 abdomen, and has a very short antecoxal piece. 



The family OAIOPHRONID^ consists of a single genus, 

 Omophron, the members of which are remarkable for their round form 

 and the fact that the scutellum is entirely concealed. They measure 

 about 6 mm. in length, and are found in holes in wet sand near the 

 margins of streams and ponds. They are found from the Atlantic to 

 the Pacific; fourteen species have been described. 



Family HALIPLID^ 

 The Crawling Water-Beetles 



This family includes a few species of small aquatic beetles, which 

 are oval, more or less pointed at each end, and very convex; our 

 larger species measure from 3.5mm. to 5 mm, in length, but some 

 are much smaller. The wing-covers have rows of punctures, and the 

 hind coxse are greatly expanded so as to conceal the basal half of the 

 hind femora and from three to six of the abdominal segments. The 

 anterior and middle tibiae and the tarsi of all of the legs are fur- 

 nished with long, swimming hairs. 



These beetles are found in ponds and streams, but most frequently 

 in spring-fed pools that do not dry^ up during the summer, and 

 contain filamentous algs and other aquatic plants. They swim 

 poorly but crawl over the stems of aquatic plants. Little is known 

 regarding the feeding habits of the adults. Matheson ('12) found that 

 several species feed on the contents of the cells of A7/e//a and the softer 

 portions of Chara and other filamentous algas. He observed also that 

 two species of Peltodytes attach their eggs to aquatic 

 plants, mainly Nitella and Chara, while Haliplus 

 ruficollis places its eggs within the dead cells of Nitella 



The larvae are aquatic, living in the same pools as 

 the adults. The body is slender; each segment except 

 the head is furnished on the back with fleshy lobes 

 with spiny tips (Fig. 565), which vary greatly in size 

 in different species; in the larvse of Peltodytes each of 

 these spines bears a long, jointed filament, which is a 

 tracheal gill. The larvae of this genus have no spiracles; 

 but the larvae of Haliplus possess both thoracic and Fig. 565. 

 abdominal spiracles. The larvae of the Haliplidce feed on filamentous 

 algse; when mature, they leave the water and each makes a cell in 

 the damp earth in which the pupa state is passed. 



About forty species of the Haliplidse have been found in our 

 faima ; these represent three genera. In Brychius, which is represented 



