NATUEAL SCIENCES OF PHILADELPHIA. 367 



Bibliography and remarks. 



1. D. vittatus ,4?/i/, H3'droc. 768; Gt/rinus vitt. Germ. sp. nov. 32; Cy- 

 cloiis opacus 'Mels., Proc. Acad. Nat. Sci. Phila. ii, 29 (faded specimens). Middle 

 and Soutliera States, not rare. 



2. D. sublineatus Aub^, Hydroc. 11o ; Giirinus suhl. Chevr., Col. Mex. 

 cent, i ; 9 -O- integer Lee , Proc. Acad. Nat. Sci. Phila. vii, 221. Arizona and 

 Lower California. 



3. D. e m a r g I n a t n s White, Brit. Mus. Cat. ; Gyrinus emarg Say, Trans. 

 Am. Phil. Soc. ii, 108 ; ed. Lee. ii, 519 ; D. americanmX Aub6, Hydroc. 777 (nee. 

 Linn.) Abundant in the middle and northern States ; for remarks on Gyrinus 

 americanus Linn., showing its probable identity with the West Indian D. 

 metallicus Aub4, see the note of Dr. Schaum in Stettin Ent. Zeit. 1848, 337. 



4. D. carolinus. I have seen but two 9 specimens, collected in South 

 Carolina; it closely resembles the preceding, but is more shining, and the api- 

 cal margin of the elytra, instead of being flat, is very narrowly refle.xed. 



5. D. serrulatus. Middle and Southern States. I have seen but two 

 (^ 9 specimens of this species, which resembles in form D. a s s i m i 1 i s , but 

 is easily distinguished by the fine serration of the apical margin of the elytra, 

 the sutural angle less prominent, the lateral flattened margin broader and more 

 reflexed, the posterior sinuosity of the eh'tra of the female much less, the striae 

 of the elytra less visible, and finally by the front thighs of the male being 

 armed with a strong sharp tooth. 



6. D. discolor .4m^/^, Hydroc. 784; Cyclous lahratiis Mels. Proc. Acad. 

 Nat. Sci. Phila. ii, 29. Abundant from Canada to Louisiana, and from Maine 

 to Kansas ; easily known by its narrower form and pale ferruginous under 

 surface ; the front thighs of the male are not toothed. 



7. D. a s s i m i 1 i s Aub^, Hydroc. 778. Cychnus ass. Kirby, Fauna Bor. Am. 

 iv, 78. Gyrinus americanus Say, Trans. Am. Philos. Soc. ii, 107 ; ed. Lee. ii, 

 519. Our most abundant species, usually known as apple bug ; extends from 

 Lake Superior to Texas, and from Maine to Kansas. The front femora of the 

 male are not toothed. 



Gyrinus Linn. 



"The species of this genus, as at present defined, are peculiar in having II 

 rows of punctures on each elytron, and an oval transverse figure limited by 

 punctures near the tip. The legs are always ferruginous, or testaceous. 

 Usually two frontal impressions and two thoracic transverse impressions are 

 well defined, but they are not equally evident in every individual, and are 

 sometimes entirely obliterated. 



"For the better definition of the species it must be observed that in those 

 in which the upper surface has a shining metallic gloss, the color becomes 

 sometimes black, and sometimes in part dark brown ; in the same proportion 

 the black color of the breast and the abdomen varies to ferruginous. The ob- 

 literation of the rows of punctures next the suture is of doubtful specific value, 

 as is also the size of the specimens, both of which characters are subject to 

 great variations." — Zimmermann, MS. To this I may add that the frontal im- 

 pressions are of no value in distinguishing species. 



On account of the close resemblance between the species, it has been very 

 difficult to identify them by the descriptions thus far published, and, as will 

 be seen in the biljliography and remarks, the determinations are frequently 

 different in each of the standard collections which have been independently 

 formed in this country. 



My own determinations are in some instances at variance with those of Dr. 

 Zimmermann and Dr. Harris, and I hope may be sustained by reference to the 

 types preserved in European collections; but at all events the possession of a 

 much larger number of specimens, from more widely separated localities, has 



1868.] 



