AMERICAN COLEOPTERA. 385 



Ab. — Thorax with a small impressed plica on either side the base. 

 H. rufieollE*. DeG. Mem. iv., p. 404; immaculicollis, Harris, N. E. Farm, 

 vii., 156. — Very similar to the other species in form, but distinct by the tho- 

 racic plica and the ill-defined elytral spots; I have seen a variety from Dakota 

 narrower and with no distinct spots (as in fluviatilis, Aube). L. - 11 — .12 inch. 



Middle and Southern States. I cannot separate American and 

 European specimens. 



H. longulus. (Lee. MSS.) sp. n.— Very close to H. ruficollis, but of a dis- 

 tinct fulvous color, less strongly punctate throughout and the thoracic plica 

 distinctly longer. L. *12 inch. 

 Lake Superior, Boston. 



CNEMIDOTUS. (111.) Er. (Type ccesus.) 

 This name was proposed for Hali.plus by Illiger and was afterwards 

 used by Erichson for this group. The elytral strife are irregular to- 

 wards the base which is explained by the tubercle visible in C. calto- 

 sus. The coloration of all the species is precisely similar, namely, 

 reddish-yellow, elytra greenish-yellow with black serial punctures, 

 suture and base more or less black, often with six black spots, three 

 in a triangle about the middle, and three in a small snb-apical triangle. 



C callosus, Lee. Ann. Lye. v., 201; simplex, Lee. 1. c. 9- — Distinct by 

 the elytra having a well marked tubercle in the males. The females are very 

 hard to separate from C. \2-punctatus. L. -12 inch. 



San Diego, (Leconte). South Carolina, (Zimmermann). 



C. 12-pimctatus, (Say) Trans Am. Phil. Soe. ii., 106. 

 Common throughout the Atlantic region ; I find every shade of 

 form in the coxal plates and cannot separate G. muticus, Lee, specifi- 

 cally. The spots vary a good deal in intensity. L. T2 inch. 



C edentulus, Lee. New Species, p. 21, 67. — Apparently distinct by the 

 more elongate form and lighter colors, and the head has the vertex black; but 

 I can find no constant character in the sculpture. L. -12 — -13 inch. 

 Middle, and Western States. 



Dytiscides. 



Epimera of metathorax triangular, visible ERETINI. 



Epimera invisible. 



Four anterior tarsi similar in the sexes, 4-jointed HYDROPOPJNI. 



Four anterior tarsi 5-jointed. 



Presternum dilated behind, truncate, meso-epimera linear. ..NOTERINI. 

 Presternum pointed. 



Two tarsal joints dilated in % AGABININI. 



Three tarsal joints dilated DYTISCINI. 



