36 [April, 



the difficulty now resting over the subject, I have thought that a series of origi- 

 nal descriptions of all the species known to me, based upon a careful comparison 

 of their specific characters, might remove some of the obstacles encountered from 

 the different style of the descriptions of different authors. I do it the more gladly, 

 as an opportunity is thus afforded me of correcting many important errors into 

 which I was led, in some of my earlier writings, by the haste and inexperience 

 of youth, from the effects of which it falls to the lot of only the most favored of 

 men to escape. 



The reader will find, in some portions of this essay, a further development of 

 the principle announced by me in a synopsis of Silphales, (Proc. Acad. 6, 275,) 

 illustrated in a genus, of which the species are very numerous ; these species 

 form small groups, according to their respective affinities, and in general the 

 limits of each species are marked by well defined organic differences. But in 

 some of the groups, occur forms so closely allied as to present, with a large series 

 of specimens, almost imperceptible differences, by which sets of specimens, at 

 first sight readily recognized and separated, become linked together. These 

 variations (in form, not color) are frequently seen to be constant in those found 

 in one locality, and in the present condition of science, would seem to indicate 

 positively the origin at different points, or at various points intermixed together, 

 of organic forms, so closely related as not to present sufficient differences to be 

 regarded as ordinary species. 



Thus it is that Nature who, not only between her works, but between her 

 processes, continually displays gradations of sublime harmony, reveals to u,s~ some 

 of the steps between those genera in which absolutely distinct species are found 

 in restricted localities, and those in which absolutely the same species are found 

 widely distributed. 



The genera known to me with the exception of a single new one, have been 

 fully described in other works, and may be thus arranged : 



Mentum dente bicuspi ; ungues plus minusve serrati : 



Paraglossae ligula non longiores .... Calathus. 



Paraglossae longiores, ultra ligulam extensae . . Pristodactyla. 

 Mentum dente simplici ; ungues simplices : 



Paraglossae ligula longiores ..... Anchus. 

 Paraglossae ligula non longiores : 



Antennae articulo 3io sequente sesqui longiore . Rhadine. 



Antennae articulo 3io sequente subaequali . . Platynus. 



Mentum dente nullo Olisthopus. 



Calathus Bon. 



1. C. gr eg ar ius, longiusculus, piceus, nitidus, apterus, thorace latitudine 

 fere longiore antice subangustato, lateribus testaceis late rotundatis, margine 

 postice latiore refiexo, basi utrinque paulo impresso, elytris striis tenuibus pro- 

 fundis, punctis tribus impressis, antennis palpis pedibusque testaceis. Long. 4. 



Dej. Sp. Gen. 3, 76; Kirby, Fauna Bor. Am. 29. 



Feronia gregaria Say, Trans. Am. Phil. Soc. 2, 47. 



Calathus distinguendus Lee. Proc. Acad. Nat. Sc 2, 53. Ann. Lye. 4, 216. 



A common species in the Middle and Eastern States, and is found occa- 

 sionally at Lake Superior. The North American species of this genus are very 

 closely allied, and seem hardly worthy of being separated; ^nevertheless, the 

 three species recognized by me in the Atlantic portion of the continent, are as 

 well distinguished from each other as from those of the Pacific coast. This one 

 will be readily recognized by the shining lustre and the moderately broad re- 

 flexed lateral margin of the thorax; in the next species the lateral margin is 

 narrower, perceptibly depressed, and not at all refiexed towards the posterior 

 angles. For authentic specimens of this species I am indebted to Dr. Harris. 



2. C. confusus, longiusculus, piceus pernitidus, apterus, thorace latitudine 

 sublongiore, antice subangustato, lateribus testaceis late rotundatis margine an- 

 gusto postice vix depresso, subrefiexo, basi utrinque paulo impresso, elytris 



