358 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



last segment curving around the base of the pleon. The epimera are 

 not evident from above. The legs (pi. VIII, fig. 46 a) are slender and 

 all terminated by a slender prehensile hand, of which the finger, or 

 dactyhis, becomes almost acicular in some of the posterior pairs. All 

 the legs are more or less hairy. 



The pleon bears on each side, near its base, a rounded lobe, which is 

 separated from the large posterior jjortion by a more or less evident 

 incision. Dorsally it is convex, and presents two hemispherical eleva- 

 tions, the proximal more convex than, but only half as large as, the 

 distal. They are separated by a broad and deep groove, and the distal 

 convexity is continued upon the obtusely-pointed apex of the pleon. 

 The operculum (pi. VIII, fig. 46 b) is vaulted ; its basal plate is rounded 

 anteriorly, carinate near its inner margin, contracted externally for the 

 distal third of its length and truncate at the tip, where it bears a stout 

 elongated-triangular finely ciliated terminal piece. The basal plate is 

 coarsely ciliated on its inner margin, and bears a few plumose hairs 

 along its outer free margin. The stylet on the second pair of pleopods 

 in the males is short and stout, surj^asses the lamella but not the cilia, 

 and is spiuulose just below the blunt apex. 



Both species are of a dull neutral color, and commonly covered with 

 particles of mud or other foreign matter. They occur on piles, or under 

 stones, in muddy places, and arc dredged on muddy bottoms. 



ZIpelys trilobus Smith (Say). 



Idotea triloba Say, Jour, Acad. Nat. Sci. Phil., vol. i, p. 425, 1818. 



Edwards, Hist. nat. des Crnst., tome iii, p. 134, 1840. 



Dekay, Zool. New York, Crust., p. 43, 1844. 



Leidy, Jour. Acad. Nat. Sci., II, vol. iii, p. 150, 1855. 

 Jaeraf triloba White, List Crust. Brit. Mus., p. 97, 1847. 

 Epelys trilobus Sniith, This Report, part i, p. 571 (277), pi. vi, fig. 28, 1874. 



Verrill, Am. Jour. Sci., Ill, vol. vii, p. 135, 1874; Proc. Amer. Assoc, 

 1873, p. 372, 1874 ; This Report, part i, p. 370 (76), 1874. 



Harger, Proc. U. S. Nat. Mus., 1879, vol. ii, p. IGO, 1879. 



Plate VII, Figs. 42 and 43. 



This species may be recognized among our Isopoda by its appearance 

 ■when seen from above, recalling the form of the trilobites, the flattened 

 dorsal surface being marked, as in those animals, by two lateral longi- 

 tudinal depressions. The x)leon is consolidated into a single piece and 

 the antenucB have only a rudimentary flagellum. It closely resembles 

 the next species, but is smaller and most readily distinguished by the 

 lateral margin of the thorax, which is, especially in the anterior part, 

 nearly even instead of zigzag from the i)rojectiug angular segments. The 

 anterior angles of the head are also less produced. 



The pleon is shorter and broader, its breadth being to its length as 

 six to ten. The deep transverse groove across the pleon is continued 

 to the margin, with only, at the most, traces of a tubercle at each side. 

 The stylet on the second j)air of pleopods of the male (pi. VII, fig. 42 6, 



