312 



Leech and Chandler: Coleoptera 



Fig. 13:11. Dytiscidae, larval structures, a, Hydrovatus con- 

 fertus; b, Copelatus parvulus, mandible and antenna; c, Cybister 

 fimbriolatus, maxilla; d, Laccophilus macu/osus, maxilla; e, 

 Thermonecfus basillaris, ventral view of labium to show ligula; 

 f, Laccophilus proximus, dorsal view of head; g, llybius sub- 

 oeneus, dorsal view of head;, h, Hydaficus sp., labium; /, llybius 

 sp., lateral view of head to show marginal keel and temporal 

 spines; /, Agabus sp., lateral view of head; k, Laccophilus sp., 

 abdominal tip and cerci; /, Agabus, abdominal tip and cerci (a,b, 

 Williams, 1936; c,d,e,f, Wilson, 1923; g,h, Bertrand, 1927; i,j, 

 F. Balfour-Browne, 1950; k,l, Wesenberg-Lund, 1912). 



its apex about on a line with hind margins of middle 



coxae; pronotum usually margined laterally 30 



— Anterior tip of metasternum depressed, with a shallow 

 pit or broad notch to receive tip of prosternal process, 

 never with a sharply outlined triangular excavation; 

 pronotum not margined 31 



30. Prosternal process flat; dorsal surface of beetle 

 unusually flat, pronotum widely margined laterally; 

 elytra lightly reticulate throughout, the meshes rather 

 coarse, unequal and irregular in shape 



Hoperius Fall 1927 



— Prosternal process convex or cariniform; elytral 

 reticulation lightly impressed, meshes of unequal 

 sizes and shapes, but very small (a superimposed 

 secondary reticulation of deeply impressed lines occurs 

 over parts of elytra of some females) 



Rhantus De jean 1 833 



31. Elytral sculpture consisting of numerous parallel 

 transverse grooves Colymbetes Clairville 1806 



— Elytra coarsely reticulate, without transverse grooves 

 Neoscutopterus J. Balfour-Browne 1943 



32. Inferior spur at apex of hind tibiae dilated, much 

 broader than the other large spur; first 3 segments 

 of front tarsi of male forming an oval plate (fig. 13:10a); 

 large beetles, 20 to 32 mm. long. CYBISTRENI 38 



— Inferior spur not or but little broader than the other; 

 first 3 segments of front tarsi of male forming a nearly 

 round plate (fig. 13:7<7); medium-sized to large beetles 



33 



33. Posterior margins of first 4 hind tarsal segments beset 

 with a dense fringe of flat golden cilia; smaller beetles, 

 about 8 to 15 mm. long 34 



— Posterior margins of first 4 hind tarsal segments bare; 

 large beetles, about 20 to 38 mm. long. DYTISCINI 



Dytiscus Linnaeus 1758 



34. Apex of prosternal process sharply pointed, pronotum 

 margined laterally; external edge of each elytron from 

 behind middle to about apical 5th margined with short 

 spines; eyes prominent; upper surface of hind tarsi 

 punctate and with fine appressed hairs. ERETINI 



Eretes Laporte 1833 



— Apex of prosternal process rounded; pronotum not 

 margined laterally; elytra without spines at sides; 

 upper surface of hind tarsi naked except for marginal 

 cilia 35 



35. Outer margin of metasternal side wings arcuate; outer 

 (shorter) spur at apex of hind tibiae blunt, more or 

 less emargiriate. THERMONECTINI 36 



— Outer margin of metasternal wings straight; outer 

 spur at apex of hind tibiae acute. HYDATICINI .... 



Hydaticus Leach 1817 



36. Elytra densely punctate, and in addition usually 

 fluted and hairy in female Acilius Leach 1817 



— Elytral punctation extremely fine or absent; some 

 females with a superimposed sexual sculpture of 

 elongate grooves, or granulate 37 



37. Elytra basically yellowish, uniformly speckled or 

 vermiculate with black; hind margin of middle femora 

 with a series of stiff setae which are only about 1/2 as 

 long as femora are wide Graphoderus Sturm 1834 



— Elytra black with yellow maculae or transverse bands, 

 or yellow with black spots, or irrorate; hind margin 

 of middle femora with a series of stiff setae which 

 are as long or longer than femora are wide (warning: 

 setae may be broken off in old or roughly handled 

 specimens) Thermonectus Dejean 1833 



38. Apex- of hind tarsi of males with 2 claws, of females 

 with a longer outer and a rudimentary inner claw 



Megadytes Sharp 1882 



— Apex of hind tarsi of males always, of females usually, 

 with only 1 claw Cybister Curtis 1827 



Key to the Known Nearetlc Genera of Dytiscidae 



Larvae 



Head with a frontal projection (fig. 13:10m); body 

 lacking lateral fringes of swimming hairs, maxillary 



palpus 3-segmented. HYDROPORINAE 2 



Head without a frontal projection; body with or without 

 swimming hairs; maxillary palpus 4- or more segmented 

 6 



