Fig. 13:58. Psephenidae. a,b,c, larva, pupa and odult of 

 Eubrianax edwardsi; d, Acneus quadrimaculatus, adult (a-c, 

 Essig, 1926; d, Horn, 1881). 



Family PSEPHENIDAE 



Water Pennies 



These oval, depressed, moderately small (6 mm.), 

 brown to black beetles (fig. 13:58) are occasionally 

 seen on the rocks along the margins of streams. 

 The adults are terrestrial but may enter the water to 

 lay their eggs. The aquatic larvae are more familiar 

 to those who sample stream life. They are commonly 

 called water pennies because of their broad flat oval 

 shape. They are found clinging to stones in slow to 

 moderately rapid streams. 



Relationships. — The genera Psephenus and Eubri- 

 anax are quite closely related, although they were 

 placed in different families for many years. Acneus 

 and Ectoparia in a general way resemble Psephenus 

 and Eubrianax both as larvae and adults but are much 

 more distantly related to them. The presence of the 

 trochantin in the adult, and the location of the gills 

 in the caudal chamber closed by an operculum in the 

 larva, are strong indications that they should be 

 placed in a separate family. The larva of Ectoparia 

 has been described in a number of publications as 

 that of Helichus (Dryopidae). 



Respiration. — When the adults enter the water to 

 deposit their eggs, they are surrounded by a film of 

 air supported by the dense body hairs. 



The larvae of Psephenus and Eubrianax have two 

 tufts of gill filaments below various of the abdominal 

 segments one to six. Spiracles are on the dorsal side 

 of the body near the base of the pleura of the meso- 

 thorax and the first eight abdominal segments. In 

 Psephenus the pleura of the eighth segment is reduced 

 or lacking, and the spiracles are on the lateral poste- 

 rior margin of the terga. 



The pupae are found on stones just above the water 

 line and have no gills. 



Larvae of Acneus and Ectoparia have three tufts 

 of retractile gill filaments which can be drawn into 

 the caudal chamber. The caudal chamber is closed 

 by an operculum. The only functional spiracles are 

 at the end of the long, curved, lateral projections of 

 the pleura of the eighth abdominal segment. What 

 appear to be scars of spiracles can be seen on the 

 dorsal side of all the abdominal segments in Acneus. 



Life history.— The adults apparently deposit their 

 eggs beneath the water on the face of stones which 

 they can reach by crawling down from the surface. 



365 

 Leech and Chandler: Coleoptera 



They are occasionally thus exposed when turning 

 stones of which only the tops protrude from the water 

 in midstream. The pupa of Eubrianax retains all ex- 

 cept the last three segments of the larval skin as a 

 shieldlike cover. The body is light colored at first, 

 except the last three segments which closely resemble 

 and replace those of the larval shield. Psephenus 

 pupate farther above the water surface. The pupae 

 are of uniform color with the last segments not replac- 

 ing those of the shield. 



Adults of Acneus are terrestrial and the larvae are 

 aquatic. The pupae are not known, but a related genus 

 Psephenoides has one of the few truly aquatic pupae 

 in the Coleoptera. It is oval and flattened like the 

 larvae with tufts of fingorlike gills along the margin 

 of the abdominal segments. 



Habitat and distribution. — This family is usually 

 found in clear, moderate to rapid streams with gravel 

 or rocky bottoms. The adults of Acneus are taken 

 along small, rapid, low elevation streams frequently 

 near waterfalls; the known larvae (all collected by 

 me) were taken in rapid sections of a stream, in pools 

 of quiet water protected from any current by large 

 boulders. It would appear that they require well- 

 aerated water, and protection from erosion or silting. 



The adults of most of the genera are occasionally 

 taken flying along the streams they inhabit. Psephenus 

 is found in the northeastern United States and from 

 California to Idaho on the west coast. In California 

 they are taken mostly at elevations below 4,000 feet. 

 Eubrianax is found throughout California up to 6,000 

 feet. Ectoparia is restricted to the northeastern and 

 central United States. Acneus is found in California 

 and Oregon up to 4,000 feet. 



Key to Neoretle Genera of Psephenidae 

 Adult* 



1. Posterior margin of prothorax smooth 2 



— Posterior margin of prothorax finely beaded or crenulate 



3 



2. Head hidden beneath the expanded pronotum; base of 

 claws with a menbranous appendage nearly reaching 

 the tip of claw Eubrianax Kiesenwetter 1874 



Eubrianax edwardsi (LeConte) 1874 (fig. 13:58a, c), 

 California, in streams 



— Head visible from above; base of claws without such 

 an appendage; northeastern and west coast of U.S. 



Psephenus Haldeman 1853 



3. Prosternum of moderate width, not depressed between 

 the coxae; claws toothed at base; antennae simple; 

 northeastern and north central U.S 



Ectoparia LeConte 1853 



— Prosternum narrow, depressed between the coxae; 

 claws slightly broader at base in female or toothed in 

 male; antennae of male flabellate; Washington to 

 California Acneus Horn 1880 



Key to Neoretle Genera of Psephenidae 



Larvae 



1. Ninth abdominal segment without a ventral operculum, 

 abdominal segments fitting tightly together to the 

 outer margin (fig, 13:59a), 4 or more segments with 

 tufts of ventral filamentous gills 2 



