612 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



Abdomen not abruptly narrower than thorax; lateral parts of third, 

 fourth, and fifth segments well developed; terminal segment conic-ally 

 produced. 



Opercular plates of the first two pairs of pleopoda and sometimes of 

 all five pairs furnished with tracheae. Inner branch of the uropoda 

 inserted far in front of the outer branch near the inner antero-lateral 

 angle of the peduncle. 



ANALYTICAL KEY TO THE SPECIES OF THE GENU8 PORCELLIO. 



a. Surface of body smooth or minutely granular. 

 b. Second pair of antenna? long, equal to half the length of the body. Flagellum 



with the first article not shorter than the second. 



c. Articles of flagellum subequal. Middle frontal lobe of head rounded; lateral 

 lobes roundly truncate. Color, dark grayish red with numerous pale, irreg- 

 ular oblong spots intermixed, arranged in two wide series separated by a 



small interval Porcellio formosus Stuxberg. 



c'. First article of flagellum of second antenme longer than the second. Middle 

 frontal lobe of head acutely produced; lateral lobes rounded. Color, dark 

 gray, with two longitudinal bands of a lighter color in wavy stripes, one on 



either side of the median line Porcellio lirvis Latreille. 



b'. Second pair of antennae short, equal to one-third the length of the body; flagel- 

 lum with the first article one-third shorter than the second. 



Porcellio panicornis Richardson. 

 a.'. Surface of body roughly granulate or tuberculate. 



b. Inner face of the mandibles with four to five penicils. Body with spots. 

 c. Third joint of peduncle of second pair of antennae furnished with a small apical 

 tooth. Frontal lateral lobes of moderate size. Color varying from gray to 

 black, with three longitudinal lines of white spots. Flagellum with joints 



subequal, or first shorter than second Porcellio rathkei Brandt 



c'. Second joint of peduncle of second pair of antenna? furnished with a large 

 apical tooth. Frontal lateral lobes large. Color, yellow; body spotted with 

 black; spots arranged in longitudinal lines. Flagellum with first joint a 



little longer than second joint Porcellio spinicornis Say 



b'. Inner face of right mandible with four to five penicils, of left mandible with 

 seven to eight penicils. Frontal lateral lobes of head large, oblique. Body 

 without spots Porcellio scaber Latreille 



PORCELLIO FORMOSUS Stuxberg. 



Porcellio formosus STUXBERG, 0fvers. Vet. Akad. Forh., 1875, No. 2, p. 57. 

 BuDDE-LuND, Crust! Isop. Terrestria, 1885, p. 141. UNDERWOOD, Bull. 111. 

 State Lab. Nat. Hist., II, 1886, p. 362. RICHARDSON, Proc. U. S. Nat. Mus., 

 XXI, 1899, p. 862; Ann. Mag. Nat. Hist. (7), IV, 1899, p. 329; American 

 Naturalist, XXXIV, 1900, p. 304. 



Localities. San Francisco and San Pedro, California. 



Body ovate, almost half as wide as long, convex, smooth, shining. 



Second pair of antennae equal in length to the width of the body; 

 the first article of the peduncle is half as long as the second, the fourth 

 has a longitudinal excavation, deep on the outside, light above, the 

 fifth is the longest, longer than the preceding by a third part, not 

 much longer than the flagellum, straight, the proximal part incon- 



