300 Coleopterological Notices, VII. 



which are rather numerous, and, at the same time, comparatively 

 feebly differentiated among themselves ; this fact becomes still 

 more notable when we consider the wide geographic range of the 

 genus. To account for these conditions we must of course as- 

 sume a very extensive extinction of intermediate types, requiring 

 considerable geologic time. In a genus whose species enjoy 

 wide range of environment, this lapse of time would, in nearly all 

 cases, bring about marked structural divergence among its com- 

 ponents, and the peculiar uniformity characterizing Omophron, 

 can be accounted for only by the universal habit of burrowing in 

 clean sand at the margin of water, which causes the environmental 

 conditions to be practically identical throughout the territorial 

 range. Heterocerus is another somewhat similar instance, the 

 environment being more varied however in this case by ample 

 and ready powers of flight. 



Our species have been totally neglected since the revision of 

 them by Dr. Horn twenty-six years ago (Tr. Am. Ent. Soc, 1870, 

 p. 71), and, as several new forms have been since discovered, the 

 suggestion of a new tabular arrangement would appear to be 

 desirable ; this is presented below : — 



Form broadly and evenly elliptical, the sides of the elytra and prothorax form- 

 ing a continuous arc; elytral stride 15 in number 2 



Form less evenly elliptical, the sides of the elytra discontinuous in curvature 



with those of the prothorax 3 



2 — Strife punctured only toward base, the sublateral obsolescent and impunc- 

 tate throughout; dark areas much predominating, blackish-brown in 



color and non-metallic laliiatiiin. Fabr. 



Striae punctured behind the middle, faint, the punctures strong throughout 

 the width, widely separated; dark areas predominating, black, highly 

 polished, with dark metallic-green reflection; body more convex. 



iiitiduni Lee. 



3 — Elytral striae 15 in number 4 



Elytral strise 14 in number 11 



4 — Dark areas of the elytra black and non-metallic, or with the feeblest recog- 

 nizable greenish reflection; dark areas generally predominant 5 



Dark areas of the elytra, black with a strong metallic-green reflection; pale 



areas frequently predominant 8 



5 — Body broadly oval, the elytra more obtuse at apex 6 



Body narrower and more elongate 7 



6 —Elytra very deeply striato-sulcate toward base, the punctures coarse, deep 

 and close-set throughout the width; intervals very convex. 



americanum Dej. 



