120 PEACH. ROOT SPECIES OF PORCET-LIO. 



species has a dusky spot below the knees which does not appear in ours. It also hag 

 a double row of whitish lines, more or less distinct, towards the outer margin, which 

 in our species is replaced by a single row of whitish spots. Other differences might 

 be specified, but these' suffice to show the glaber distinct from its European 

 analogue. 



The Unspotted Porcellio (P. immaculatus) is dull blackish brown or leaden 

 brown with faint short pale lines and the middle of each segment rough from elevated 

 granules; under side and legs white or lurid. Length 80 or less. This is readily- 

 discriminated by its uniform brown color unvaried by spots or stripes save the short 

 longitudinal lines which are so faint as scarcely to be perceived and are frequently 

 wholly wanting. It is also our smallest species. It probably occurs throughout the 

 United States, for I met with it in Illinois, and specimens have also been sent me by 

 Mr. Robertson ftom west of Arkansas. 



The Striped Porcellio (P. viltatus) is black or leaden blackish with the head 

 deeper black and the under side whitish ; the segments are rough from elevated gra- 

 nules with their hind margins smooth ; along the middle of the back is a row of white 

 spots and another more distinct near the outer margin; these spots are often conflu- 

 ent, forming continuous stripes. Length 6.35. The same pale short longitudinal 

 lines which are common in other species are more or less perceptible in this also. 

 Young individuals are of a pale or even whitish color but show the usual stripes of a 

 more clear white. It is one of our most common species. 



The Mottled Porcellio (P.mixtus) is tawny yellow variously dotted and spotted 

 with black, and with a row of whitish spots which are often confluent into stripes 

 along the middle of the back and near the outer margin; outer edge pale, at least on 

 the angles of the segments; segments rough from elevated black granules, their basal 

 .and apical margins smooth. Length 0.40. The elevated granules form round and 

 oblong black dots, and often on each side of the back the intervals between them are 

 white, thus presenting short longitudinal lines of this color, and in a variety (varie- 

 galas) these lines are confluent, forming a longitudinal row of white blotches be- 

 tween the dorsal and lateral stripes. Sometimes the stripe on the middle of the back 

 is tawny yellow instead of whitish. This appears to be the most rare of any of our 

 species. 



The Pretty Porcellio (P. limatus). Black or blackish, with a stripe each side 

 and the outer margin broadly whitish, and two rows of bright yellow spots alon" the 

 back; the segments rough with raised granules over their whole surface. Length 

 0.60. This is our most common species, being thrice as numerous as any other. It 

 occurs in abundance in our cellars and under stones and billets of wood in the yards 

 about dwellings and barns. It is quite variable in its colors. In young individuals 

 the two rows of spots along the back are pale or whitish . As it increases in size they 

 all gradually change to yellow, or one or two of these §pots take on a bright yellow 

 color whilst the rest remain whitish, hut this yellow color is suet essively assumed by 

 the others, and in old individuals the whole become of a vivid ochre yellow. Dots 

 of this same color sometimes appear also upon the narrow posterior or caudal seg- 

 ments prolonging the rows to the tip of the body. The following varieties of this 

 j^cies may be distinguished. 



