48 TIIOS. L. CASEY. 



than long, iinpunctate, and highly polished. Elytra at base as wide as the 

 contiguous prunotum ; sides parallel for four-fifths the length from the 

 humeri, evenly and very strongly arcuate ; disk very obtusely rounded 

 behind when viewed vertically, t^ro and one-third times as long as the 

 pronotnm ; snrface minutely and regularly creased, very minutely and 

 strongly granulated, rather feebly and minutely punctate ; punctures ar- 

 ranged in regular striae, with a single row of smaller punctures between. 

 Under surface of tlie abdomen very sparsely and feebly punctate, except on 

 the last segment, where they are deep, dense, and setigerous. Legs mode- 

 rate ; tarsi short and robust, second and third joints of the posterior very 

 feebly elongated. Length 13.5-15.0 mm. ; width at widest section, wliich is 

 at the middle of the elytral suture as viewed vertically, G. 4-7.0 mm. 



Arizona ; two specimens ; differences scarcely noticeable. 



Regarding the elytral suture of this si)ccies as a line in space, its 

 course is seen to be nearly straight to within a very short distance 

 of the elytral apex as viewed vertically, where it is suddenly bent 

 downward, so that at the immediate apex of the elytra, its course 

 makes an angle perceptibly less than a right angle, with its direction 

 at the scutellum. In no other species that I have seen is the sutural 

 line so strongly and suddenly bent posteriorly ; there is no tendency 

 to caudal prolongation. 



This species is more closely allied to extricata Say than any other 

 species in the catalogue, and differs in the following very important 

 characters : — 



In extricata the intercoxal salient of the first ventral segment is 

 about as wide as the intercoxal salient of the metasternum, while in 

 arcuata the first is very much wider than the second, and is relatively 

 much shorter. 



In the former species the intercoxal process of the prosternum is 

 very abruptly constricted posteriorly, into an elongated, narrow pro- 

 cess, while in the latter it is very gradually and arcuately narrowed 

 posteriorly. 



In the former the second joint of the antennae is about one-fifth 

 as long as the third, and is wider than long, while in the latter it is 

 more than one-fourth as long as the third, and is nearly as long as wide. 



The elytral j)unctuation in the two species differs in (juality to a 

 marked degree ; in extricata it consists of approximate rows of very 

 approximate punctures, with more widely spaced punctures between 

 the rows; in arcuata it consists of widely spaced rows of approximate 

 punctures, with regular rows of much more distant [lunctures between 

 them. 



The form of body is quite different in the two species ; that above 

 described greatly resembles coynata Ilald., if the type of tiie latter 



