164 
CHARLES W. LENG. 
Posterior femora pednncnlate ; thorax closely punctulate. 
Legs (lark ; posterior femora deiitate in both sexes eiimi’siiiata. 
Legs (lark ; posterior femora dentate in male only iiiof allica. 
Legs rufo-testaceous ; posterior femora dentate in both sexes flavipoN. 
Posterior femora elliptical ; dentate in both sexes; thorax sparsely punctured ; 
legs rufo-testaceous riifa. 
Tlie species contained in this group may be arranged in jtairs as 
placed above ; the differences, however, between pudlla and /(?Hior«^hs, 
emcirginata and metallica, jiavi2)es and rufa, are feeble. The first 
pair are readily isolated by the depressed thorax, the second by the 
dark legs, the third by the yellow legs and more convex thorax. It 
must be observed that the femoral tooth is less developed in the 
females throughout the genus, and is particularly weak in this group ; 
femora are subject to some variation in form and the punctuation is 
inconstant in many of the preceding species, so that, while the con- 
siderable number of specimens before me are separable by the char- 
acters given, the reader must be prepared to find some which, in 
these respects, will vary from the tyj)ical form. 
Descriptions and Notes. 
In the following pages I propose to copy either the original de- 
scription, or that of Dr. LeConte’s paper, su})plementing each with 
descriptions of those parts especially useful in recognizing the si)ecies 
and stating the sexual differences and the variations I have observed. 
The bibliography and synonymy is placed at the end. 
I>. liirticollis Kirby. Original description. 
“Downy satiny underneatb and silvery, elytra naked, black with tbe punc- 
tures of tbe rows green gilt ; posterior tbigbs unidentate. Length 3.5 lines. A 
single specimen taken in lat. 65°. 
“ Body underneatb covered with a thick coat of decumbent pile resembling 
.satin and shining like silver. Head hoary from inconspicuous bair.s, most mi- 
nutely and couflueutly punctured with a slight interocular channel with an 
obtuse ridge on each side; antennse with tbe second and third joints equal in 
length, auburn glittering with silver pile; i)rothorax longer than wide, hoary 
from inconspicuous down, most minutely and confluently punctured, channeled, 
sides subimpressed, anterior tubercles flat; scutellum large, levigated; elytra 
black, punctured in rows, whose interstices are wrinkled ; posterior tbigbs with 
a single short obtusangular tooth. This jiretty species comes near bidens Oliv., 
which I always find on Potamogeton natans, but it is sufficiently distinguished by 
its black thorax hoary from down and legs without any red.” 
Jfesosferjiim narrower than tbe coxa ; first ventral segment nhont equal to tbe 
metasternum ; form moderately flattened above and beneath ; third joint of an- 
tennse e(iual to or slightly longer than tbe second. 
