158 



THE MYRIAPODA OV NORTH AMERICA. 



S. POLYMORniA. 



S. olivaceo-brunnca ; oapite dilute castanco ; scgmento ceplialioo subovato, posticc subtrunoato, fere impunc- 

 tato ; antonnis 30 artieulatis ; dentc mandibulari tuborculo basali magno ; dentibus labialibus 8, maximis, duobus 

 intirais utrinquo eoadunatis, externis sejunetis ; aoutis interdum margine posteriore nigro-viridc, marginibus 

 lateralibus plerumque liberis; pedibus postremis robuatis, supra subcomplanatis; artioulo basali subdeprcsso, 

 intus 3 — 7 spinis, subtus 10 — 18 spinis in seric quadruplici (interdum inordinatim) dispositis, processu angular] 

 aut bifido aut trifido aut quadrifido; appendicibua analibus lateralibus aingula 4 — 8 spinis apicalibus ct altera 

 marginal!. 



Olive-brown; head light chestnut; cephalic segment subovato, posteriorly subtruncate, almost impunctato; 

 antenna 30 articulate ; mandibular tooth with a largo basal tubercle ; labial teeth 8, very large, the inmost two 

 on each side coadnate, the external distant; scuta sometimes with the posterior margin blackish-green, the lateral 

 margin generally free; last pair of feet robust, above subcomplanatc ; basal joint, and median also, subdepressed, 

 within with 3 — 7 spines, below with 10 — 18 spines arranged in a fourfold series (sometimes irregular), angular 

 process either bifid, trifid, or quadrifid; lateral anal appendages, each with 4 — 8 apical spines and a mar- 

 ginal one. 



S. TOLYMOEPHA, Wood, Proc. Acad. Nat. Sci., 1861, p. 11. Journ. A. N. S., new series, 1863, p. 20. 



The prebasilar fold is apparent but connate with the rather large; basilar segment. 

 The first segment of the body is very small ; the scuto-episcutal suture are barely trace- 

 able, but the sterno-cpisternal are much more distinct. In a few individuals the labial 

 teeth are small and coadnate. The color shades off from that given above to a testaceous 

 chestnut. This species is closely allied to S. heros, and perhaps a differential diagnosis 

 would not be amiss. The most important difference is in the number of joints to the 

 antenna?. Owing to the case with which these animals lose portions of these organs, 

 the want of the typical number is not to be relied on in the identification of individuals. 

 Another character which also is often not available for individual identification, but 

 which characterizes this species, is the small size attained to. The spines of the lower 

 surface, of basal articulations of last pair of legs, arc more numerous than in S. heron, 

 and arranged in four rows instead of three. The difference in arrangement is, perhaps, 

 more apparent than real ; the homologue of the first row of spines existing in some 

 specimens of S. heros, but being placed a little higher up, they are thrown with those on 

 the inner side of the limb. The angular process has fewer spines than in & heros. 

 Finally, although the species do exist on common ground, yet heros is a more tropical 

 and poh/morpha a more boreal animal, the regions which they occupy merely overlapping 

 somewhat. Length 3^ inches. 



