1873.] 4-3 [Horn> 



The last three species need no special comment, their characters being: 

 abundantly sufficient to distinguish them from any in the genus. The 

 species in Section A are arranged as nearly as may be in such a sequence 

 that the gradual obliteration of the thoracic vitta? may be shown. S. sem 

 imitates the markings of cicatricosus of the preceding group, but the vittse 

 are much less elevated ; scoparius is also similar, but the markings 

 still more reduced. The next three species are always densely clothed 

 with the argillaceous indument which almost entirely obliterates all 

 sculpture. S. callosus has the thoracic punctures-very larje, being really 

 erosions which are more or less confluent ; sculptilis is punctured and not 

 eroded, and has the elytral intervals flat. S. melanocephalus may readily 

 be known by the median vitta being reduced to a narrow carina slightly 

 dilated at tip, and which is situated at the anterior half of the median 

 line, and on each side of which is a small callus. 8. Sayi has the median 

 vitta feeble but entire, and differs but slightly from the next species. The 

 specific name placidus is chosen for an abundant and very variable form 

 which has received many names, as it is the name by which it has come 

 to be known to most of our entomologists. It may at all times be known 

 by the median vitta of the thorax being bifurcate in front and between 

 the two branches, immediately behind the apical constriction is a shallow 

 fossa more or less marked, in which the punctures are denser and deeper. 

 Among the species without the usual thoracic vitta 1 , gentilis is known by 

 the deep elytral striae which are as wide at bottom as at top, punctures 

 not very evident, thorax coarsely and densely punctured, median fine 

 line smooth; parvulus recalls placidus, and has the femora very coarsely 

 foveato- punctate ; retusus is a robust form with indistinctly defined, 

 fusiform, impunctured thoracic space; arizonensis has the thorax com- 

 paratively finely punctured and all the elytral sculpture neatly defined ; 

 gagatinus is more attenuate posteriorly than any of the preceding, and 

 the thorax shining with the punctures unevenly distributed. 



S. zese Walsh, Practical Entomologist, II., p. 117 ; Riley, Third 

 Annual Report, 1871, p. 59, fig 2'2. 



Black, shining. Rostrum three-fourths the length of thorax, slender, 

 slightly compressed, finely, at base more coarsely punctured, not canalicu- 

 late, and with a moderate puncture between the eyes. Thorax longer 

 than wide, anteriorly constricted, sides gradually arcuate in front, at 

 middle sub-parallel, base slightly narrower ; sui-face with three elevated 

 vittse, as follows : median entire, very slender at each end, broadly 

 dilated in front of middle, lateral vitta sinuous, interrupted opposite the 

 broad portion of the median vitta, and with an oblique broad branch 

 from the posterior portion extending toward the basal angle ; spaces be- 

 tween the vittse veiy coarsely, sub confluently punctured. Scutellum 

 slightly concave. Elytra oval, emarginate at base, surface finely striate, 

 and with large fovese rather irregularly placed along the striae, becoming 

 reduced to punctures toward the apex ; intervals flat, very nearly 

 equal, uni-seriately punctured, a slight callosity at humerus and tip of 



