309 

 Leech and Chandler: Coleoptera 



she lives without food for nearly a year, being sus- 

 tained by food reserves derived from the breakdown 

 of her wing-muscles." It will thus be of value to 

 record what species actually fly to lights, or land on 

 the shiny tops of cars, mistaking them for water. 



Most species crawl or run easily on dry land; some, 

 especially Laccophilus spp. and Hydrotrupes palpalis 

 Sharp, can jump almost like flea-beetles. 



Dytiscidae occur on all the major land masses 

 and on a fair number of oceanic islands. Many of the 

 genera are widespread; of the eleven listed by J. 

 Bal four-Browne from Oceania, seven occur in Cali- 

 fornia, and of the nineteen cited by him and by Brinck 

 for Manchuria, all but one occur in California. The 

 species of Matus are found in the triangular area 

 bounded by southern Ontario, Texas, and Florida; 

 the only other known genus in the tribe, Batracho- 

 matus, is confined to the Australian region. One 

 species, Eretes sticticus (Linnaeus), is almost cos- 

 mopolitan, and has been taken in southern California. 



Taxonomic characters. — In many genera specific 

 separations are based on the secondary sex char- 

 acters of the males. These are most often seen as a 

 broadening of the front and/or middle tarsi, toothed 

 or otherwise modified tarsal claws, smooth and shiny 

 rather than rough or dull elytral and pronotal sculpture, 

 enlarged antennal segments, peculiar forms of the 

 tibiae and femora, or differences in sculpture of the 

 last abdominal sternite. The male genitalia show 

 specific characters within most genera of Laccophi- 

 linae, Hydroporinae, and Colymbetinae, but probably 

 not in the Dytiscinae except for the genus Dytiscus. 

 The dorsal color pattern is helpful in genera such as 

 Hydroporus, Hygrotus, Rhantus, Thermonectus, and 

 Dytiscus. 



Key to the Genera of Dytiscidae of the 



United States and Canada 4 



Adults 



1. Middle of prosternum and its postcoxal process (fig. 

 13:8a) in same plane; front and middle tarsi distinctly 

 5-segmented, segment 4 approximately as long as 3; 

 scutellum fully exposed (fig. 13:7i>) or concealed .. 17 



— Middle of prosternum not in same plane as its process 

 (fig. 13:86); front and middle tarsi 4-segmented, or 

 5-segmented with 4th very small and almost concealed 

 between lobes of 3rd (fig. 13:7<i); scutellum concealed, 

 except in Celina spp. which have elytral apices and 

 apex of last abdominal sternite acuminate. Subfamily 

 Hydroporinae 2 



2. Scutellum fully visible; apices of elytra and last 

 abdominal sternite produced, acuminate. METHLINI 

 (fig. 13:146) Celina Aube 1837-38 



— Scutellum covered by pronotum; apices of elytra 

 rounded, subtruncate, or acute 3 



3. Episterna of metathorax not reaching middle coxal 



4 The taxonomy of the Hydroporinae is still unsettled, and can 

 not be solved by study of any one continental fauna. The present 

 key does not recognize all genera proposed for Nearctic species. 

 The Oreodytes picturatus (Horn) of this paper is the type of the 

 genus Deuteronectes Guignot 1945, and O. abbreviatus the type 

 of Nectoporus Guignot 1950. Deronectes quadrimaculatus (Horn) 

 has sometimes been placed in Neonectes Zimmermann, the type 

 of which is Hydroporus natrix Sharp 1884, from Japan. 



Fig. 13:8. Ventrolateral view of thorax showing relationship of 

 middle of prosternum to its postcoxal process, a, Laccophilus 

 decipiens; b, Hygrotus unguicularis (Leech, originals). 



cavities (fig. 13:9), being excluded by mesepimera (VA- 

 TELLINI). Prosternal process short, broad, not reaching 

 metasternum, its tip ending at front of the contiguous 

 middle coxae Derovatellus Sharp 1882 



— Episterna of metathorax reaching middle coxal cavities; 

 apex of prosternal process reaching metasternum ... 4 



4. Broad apex of hind coxal processes conjointly divided 

 into 3 parts: 2 widely separated narrow lateral lobes 

 and a broad depressed middle region (fig. 13:13c) 

 (HYDROVATINI). Small broadly ovate beetles about 

 2.5 mm. long Hydrovatus Motschulsky 1855 



— Hind coxal processes not divided into 3 parts as 

 described above, but either without lateral lobes, or 

 with these lobes covering bases of trochanters 5 



5. Hind coxal processes without lateral lobes, bases of 

 hind trochanters entirely free (fig. 13:7e) 6 



— Sides of hind coxal processes divergent, more or less 

 produced into lobes which cover bases of hind tro- 

 chanters. HYDROPORINI (fig. 13:7^) 11 



6. Hind tibiae straight, of almost uniform width from 

 near base to apex; hind tarsal claws unequal; pros- 

 ternal process short and broad, or rhomboid; epipleura 

 with a diagonal carina crossing near base; glabrous, 

 ovate, ventrally convex beetles. HYPHYDRINI 7 



— Hind tibiae slightly arcuate, narrow at base, gradually 

 widening to apex; hind tarsal claws e^ual; prosternal 

 process oblong; epipleura without a diagonal carina 

 near base (except in Brachyvatus). BIDESSINI 8 



7. Middle coxae separated by about width of a middle 

 coxa; prosternal process short and broad, apex obtuse 

 Pachydrus Sharp 1882 



— Middle coxae separated by only 1/2 the width of a 

 middle coxa; prosternal process rhomboid, apex acute 

 (fig. 13:15a 7 ) Desmopachria Babington 1841 



8. Each elytron with a sharp narrow carina, starting at 

 base opposite pronotal plica and fading out at declivity; 

 pronotum transversely impressed at base 



Anodocheilus Babington 1841 



— Elytra without sharp narrow carinae, though often 

 with a short basal groove opposite each pronotal 

 plica; pronotum not transversely impressed at base 



9 



9. Hind coxal lines strongly sulcate-impressed, parallel 

 posteriorly, converging as they continue forward 

 across mid-metasternum to meet at middle coxae (fig. 

 13:136); front and middle tarsi clearly 5-segmented 

 Bidessonotus Regimbart 1895 



— Hind coxal lines not continued anteriorly across 

 metasternum; front and middle tarsi apparently 4- 

 segmented 10 



10. Epipleura crossed near base by an oblique carina 



Brachyvatus Zimmermann 1919 



— No oblique carina near base of epipleura (fig. 13:14c, e) 



Bidessus Sharp 1 882 



11. Bases of hind femora contacting hind coxal lobes 

 Laccornis Des Gozis 1914 



— Hind femora separated from hind coxal lobes by basal 

 part of trochanters 12 



