70 NORTH AMERICAN 



Male — Posterior edge of the fifth ventral segment emarginate in its mid- 

 dle half, emargination evenly rounded and just perceptible; sixth segment 

 broadly sinuate at apex, sinus very wide, somewhat acutely rounded at the 

 bottom, and eight times as wide as deep. 



Female. — Sixth segment evenly rounded behind. 



Length 2.5 mm. 



Batclieliwauung Bay, Lake Superior, 2. 



51. S. plllto n. sp. — Form robust. Pubescence very short and sparse, 

 sub-recumbent, pale rlavo-cinereous. Head very small, slightly more than 

 twice as wide as long ; interocular surface distinctly convex, more than 

 twice as wide as the eye ; longitudinal elevation wider than the lateral por- 

 tions, feebly convex ; sulcations feeble, punctures coarse, rounded, evenly 

 distributed, interspaces nearly one-half as wide as the punctures, very con- 

 vex, polished ; ocular lines meeting at somewhat less than two lengths in 

 advance ; antennae distinctly longer than the width of head, robust, club 

 distinct, first and second joints nearly black, remainder rather dark piceous- 

 brown ; third, fourth, and fifth joints uniformly and rapidly decreasing in 

 length, sixth and seventh abruptly shorter, equal in length, cordate, the 

 latter slightly thicker, eighth as thick as the seventh, globular, joints of club 

 increasing rapidly in length and thickness ; maxillary palpi rather short 

 and robust, piceous-black, first joint rather pale piceo-testaceous. Prothorax 

 widest slightly before the middle, where it is very slightly narrower than 

 the head and distinctly narrower than long; sides thence feebly convergent 

 posteriorly and nearly straight ; anterior and posterior margins sub-equal in 

 length, the former slightly the more arcuate; surface rather strongly tuber- 

 culate near the basal angles, mere convex in the middle, closely, very finely, 

 deeply, and irregularly punctate ; canaliculation narrow, somewhat distinct, 

 terminating at equal distances from the base and apex, nearly three-fourths 

 as long as the pronotum. Elytra at base much wider than the head ; sides 

 feebly divergent posteriorly, slightly longer than the width at base, and 

 strongly arcuate ; together roundly and somewhat feebly emarginate behind ; 

 suture nearly one-fourth as long again as the pronotum ; surface narrowly 

 and feebly impressed along the suture, deeply, very closely, rather finely and 

 exceedingly irregularly channeled, interspaces convex and highly polished. 

 Abdominal segments decreasing very uniformly and rather rapidly in width, 

 first slightly narrower than the contiguous elytra ; surface polished, finely 

 and sparsely punctulate ; transverse carinae 4-cuspid, cusps equal in length, 

 equidistant, rather long, fine and generally enlarged slightly at the tips. 

 Legs slender, piceous-black ; first joint of the posterior tarsi short, four- 

 fifths as long again as the second, distinctly shorter than the fifth, second 

 and third equal, fourth slightly shorter, as wide as long ; tarsi nearly cylin- 

 drical throughout. 



Mali . — Posterior edge of the fifth ventral segment just perceptibly emargi- 

 nate in the middle ; sixth segment very broad at apex, where it is broadly 

 sinuate, sinus occupying nearly the entire segmental apex, evenly rounded, 

 and about eight times as wide as deep ; seventh broad and truncate at tip, 

 lateral setae moderately developed. 



Female: — Sixth segment very broad, evenly rounded behind. 



Length 2.7-2.8 mm. 



