119 



Abstract of a Memoir on the Pselaphid^e. 



I would invite the attention of observers to the fact, that the antennae of the 

 genus Bryaxis are provided with only two joints, when the medial thoracic fovea is 

 larger than the lateral ones, or when these last are entirely wanting. I have not yet 

 succeeded in finding which joint becomes obsolete, but it would be very interesting to 

 follow up this investigation by the aid of foreign species, and to ascertain whether 

 other forms than those specified are also embraced in the division with ten-jointed 

 antenna?. The genus Batrisus having been very much increased, it became necessary 

 to search for some means of dividing it into groups, and the structure of the front has 

 enabled me to do this in a tolerably natural manner. 



The parallelism of the productions of the two continents is seldom more beauti- 

 fully displayed than in the present group. There is now but a single European genus 

 (Bythinus), which has not its representative or its analogue in this country. This cor- 

 respondence extends in a remarkable manner through the species of which the genera 

 are composed, so that almost every species of the genera common to the two continents 

 has its exact equivalent : moreover, in those genera which, from possessing less power 

 of variation, consist only of a single species, the parallelism of characters is still kept 

 up to a most surprizing extent ; so much so, that if we were to leave out all strictly 

 generic characters, the two analogues would be represented by a single diagnosis. 



In addition to these equivalents and analogues, we have still remaining many ge- 

 nera and species without representatives in Europe, a fact which leads me to infer 

 that the total number of species of Pselaphidae in North America, notwithstanding the 

 rarity of individuals, is larger than in the corresponding part of the other continent. 



Notwithstanding the difference in the structure of the palpi, I have placed Ceo- 

 phyllus as the American analogue of Chennium. The form of the body, and in fact 

 the external characters, are exactly similar in the two genera. And on account of the 

 variation of the cephalic organs, and especially of the palpi (as noticed in Tychus and 

 ' Ctenistes) it is obvious that a similarity of structure is not necessary to a strong affinity 

 between two species; and I have in this instance considered it of secondary importance, 

 as compared with the general habit, and very particular structure of the antennas. 



It will be observed, too, in comparing a number of species of any genus of Psela- 

 phidae, that however much the relative proportions of the joints of the antennae vary, 

 there is still a particular appearance, depending perhaps on the method of articulation, 

 which enables a practised eye at once to recognize the antennae of each genus. On 

 this account I have beeu led to consider in this group the structure of the antennae as 

 of fundamental importance in arriving at a philosophical arrangement of the genera 

 in their mutual relations. 



The differences already alluded to are, however, so slight as scarcely to be appre- 

 ciated in a description. Not so with the manner of insertion of these organs; here 

 we find great and important variations : some having the antennae inserted under the 

 front, as in many Brachelytra; while others have the front porrected aud elevated into 

 a narrow tubercle, upon or under which the antennae are inserted. 



Using this principle of division, the genera fall into two very natural series, which 

 to some extent repeat each other.* 



* Another reason why I consider the position of the antennae as of primary impor- 

 tance in the division of this group, rather than the number of their articulations, and 



