THE MYKIAPODA OF NORTH AMERICA. 225 



large, and distally very hairy. They are each armed with two large and two small spines. 

 The longer and more slender of the former at its proximal portion is bent rather abruptly 

 at right angles to itself, but is nearly straight afterwards. The more robust is nearly 

 straight, save at its distal extremity, where it is abruptly bent at right angles to itself. 

 It is armed with several very slender spinules, and has one edge distantly and obsoletely 

 denticulate. Of the smaller spines, one is short and blunt ; the other much longer, sharp, 

 slender, and falciform. The last scutum is triangular, and has its apex truncate and very 

 slightly decurvate. The preanal scale is semi-orbicular. Length, 2 to 3 inches. 



Hub. Mississippi. — Museum of Smithsonian. 



Subgenus LErTODESM US. 

 Corpus subcyliudricum. Dorsum valde convcxum. Laminae laterales parvae. 

 Body subcylindrical. Dorsum very convex. Lateral laminre small. 



P. PLACIDUS. 



P. olivaceo-brunneus, seutis plerumque nigra vittatis; laminis lateralibus parvis, dilute brunneis; pedibus satu- 

 rate olivaceis; sternis dilute brunneis; appendiuibus (Fig. 5G) masculis, valde elongatis ; spina terminate magna, 

 in spiram ducta et spinulo basali longissimo falciforme et altero laterale breve robusto instructa, margine partim 

 acute serrato, partim integro. 



Olive-brown; many of the scuta banded with black; lateral laminee small, light-brown; sterna light-brown; 

 male appendages strongly elongate; terminal spine large, spiral, furnished with a very long, falciform, basal 

 spinule, and a second short, robust, lateral one; its margin partly entire, partly acutely serrulate. 



P. placidus, Wood, Proc. Acad. Nat. Sci., 1864, p. 9. 



The head is dark-colored. Besides its median furrow, it is ornamented witli a pair 

 of sometimes illy pronounced puncta on each side of the vertex. Its inferior border is 

 rather broadly emarginate. The antenna? are elongate, dark-brown, and 

 tipped with black. The anal scutum agrees with the others in color. It 

 is triangular, with its apex truncate, obscurely emarginate and decurvate. 

 The male genital appendages are strikingly elongate. The terminal spine 

 is nearly black. It is bent spirally on itself, but after performing a little 

 more than an entire turn is nearly horizontal for some length. It is flat- 

 tened, with its superior surface somewhat umbonate, and ends in a thick, 

 blunt, spine-like process. The proximal portion of the anterior margin is 

 acutely serrate. From the edge projects a short thorn-like spinule. and 

 from the base a long, slender, falciform spine. Length, 1J inches. 



Hab. Michigan.— Prof. Miles. 

 vol. xin— 29 



