The Pselaphid^ of North America. 219 



the side pieces not distinct, ankylosed, prosternum very narrow, 

 often not visible between tlie coxre. Mesosternum very short, 

 metasternum very broad. Elytra truncate, subtriangular. 

 Abdomen with live dorsal and hve or six ventral segments. 

 The anterior coxa? are prominent, conical, nearly contiguous, 

 the intermediate rounded and near together, the posterior ones 

 transverse, not prominent. 



The Pselaphidai proper are divided into three sections, the 

 Pselaphini, Bryaxini, and Euplectini which sections become 

 almost yearly more indennite by the discoverv of inter- 

 mediate forms, thus demonstrating the unity of the present 

 famih'. 



The Pselaphini were formerly considered a well defined 

 section, but later discoveries such as the Bythinoid forms of 

 Machajrodes, Eutrichites and Scalenarthrus link them with 

 the Bryaxini. The genera Pselaptus, Verticinotus, and 

 Eupsenius on one hand and Arthmius on the other lead from 

 Bryaxis to Batrisus and the general form of the latter is 

 repeated in Trimium. For want of a better place, the 

 Trogasterini arc placed between Trimium and Euplectus, as 

 they exhibit radiating affinities. 



The species of the second section of Capt. Casey's synopti- 

 cal table are in our opinion not Euplecti. They stand between 

 Euplectus and Trimium, nearer the latter, and have received 

 the name Trimioplectus. 



The forms of Eutyphlus, Thesium and FaUscus approach 

 the Faronii which latter we leave intact under the old genus 

 Faronus for want of a more complete knowledge of the 

 foreign members of this section. 



All of the Pselaphidee live on animal substances, and the 

 comparatively powerful mandibles and maxillae together with 

 long palpal members seem to indicate that they capture fleet 

 and hard-shelled prey. As a rule the Pselaphini live mostly 

 in pairs while all the others are gregarious at least during the 

 period of copulation when so-called " rare " species may be 

 found in numbers. 



