NO. 2222. NORTH AMERICAN ONYCHIURINAE—FOLSOM. 645 



25 to 35) simple peripheral tubercles, Pseudocelli of head as follows: 

 Antennal base, 3+3 (fig. 44) arranged in a triangle on each side; 

 posterior border of head, 3+3, occasionally 4 + 4. Antennae almost 

 as long as the head. Sense organ of third antennal segment (fig. 45) 

 with five (abnormally six) papillae, five guard setae, two sense rods, 

 and two capitate tuberculate sense clubs. Pseudocelli of body 

 (fig. 5) as follows — Prothorax: dorsal, 0; lateral, (proximal pre- 

 coxal), 1 + 1. Mesothorax: dorsal, 2 +2; lateral (proximal precoxal), 

 1 + 1. Metathorax: dorsal, 3 +3; lateral (proximal precoxal), 1 + 1. 

 First, second and third abdominal segments: dorsal, 3 + 3. Fourth 

 abdominal : dorsal, 3+3; postero-lateral, 1 + 1. Fifth abdominal: 

 Dorsal, 3+3; antero-lateral, 1 + 1 ; the three dorsal on each side lying 

 close together in a straight line. Sixth abdominal, 0. Unguis 

 (fig. 46) curving, untoothed, or minutely unidentate one third from 

 apex, especially on the front feet. Unguiculus gradually tapering, 

 distally attenuate, as long as, or a little longer than, the unguis. 

 Furcula represented by a crescentic fold (figs. 47, 48); tenaculum 

 absent. Anal spines (fig. 49) two, large, almost as long as hind 

 ungues, arcuate or almost straight, on prominent papillae one-third 

 as long as the spines. Clothing (fig. 50) of numerous short curving 

 setae and fewer long stiff setae, becoming longer on the posterior 

 part of the abdomen. Cuticular tubercules moderate in size (fig. 51). 

 Length, 1.8 mm. 



In one specimen the right sense organ of the third antennal seg- 

 ment showed six papillae (fig. 45). Agren ('03, p. 128) mentions the 

 occurrence in one specimen of seven papillae and tliree sense clubs. 



According to European WTiters (see Agren, '04, p. 12) the pseu- 

 docelli of the antennal base are rarely four on each side; those of the 

 posterior border of the head varying from two to four on each side; 

 of the mesonotum, one to thi'ee; metanotum, one to three; fourth 

 abdominal segment, three or four, rarely two; and those on the 

 posterior part of the fifth abdominal segment, two to four on each 

 side. These variations I have not yet found in this country. 



The unguiculus varies a little in length, extending sometimes not 

 quite as far as the unguis. 



My North .\jnerican specimens agree accurately with European 

 descriptions and with European examples sent to me by Dr. Caesar 

 Schaffer. 



The form that Guthi'ie ('03, p. 97) termed amhulans is armalus, as 

 I have found by an examination of nine of his specimens, sent to me 

 by Prof. Henry F. Nachtrieb. 



Agren ('04, p. 12) found, from his study of the type material, that 

 0. ardicus Tullberg is not specifically distinct from 0. arwatus 

 Tullberg, being simply a large vari(^ty, 3.5 mm. in length (maximum 

 length, 4.1 mm., according to Skorikow). 



