MARINE ISOPODA OF NEW ENGLAND, ETC. 355 



distinguishes them at once from young specimens of Idotea, especially 

 I. pliospliorea, which sometimes resemble E. filiformis. This character 

 of the antennae serves, indeed, to distinguish the two unlike representa- 

 tives of the present geuus from all the other Isopoda of our coast. 



Erichsonia filiformis Harger (Say). 



Stenosoma filiformis Say, Jour. Acacl. Nat. Sci., vol. i, p. 424, 1818. 



Edwards, Hist. nat. des Crust., torn, iii, p. 134, 1840. 



Dekay, Zool. New York, Crust., p. 44, 1844. 

 Idotea filiformis White, List Crust. Brit. Mus., p. 95, 1847. 



Erichsonia filiformis Harger, This Report, part i, p. 570 (276), pi. vi, fig. 26, 

 1874; Proc. U. S. Nat. Mus., 1879, vol. ii, p. 160, 1879. 



Verrill, This Report, part i, p. 316 (22), 1874. 



PLATE VII, FIGS. 38-41. 



This species may be at once distinguished from the following by the 

 strongly serrated outline of the sides, as seen from above. The clavate 

 terminal segment of the antennas distinguishes it from the other known 

 Isopoda of our coast. 



The body is slender and elongated, but less so than in the next spe- 

 cies, the sides are nearly parallel and there is a median row of promi- 

 nent tubercles, one, large and bifid, on the head, and one upon each 

 thoracic segment. The eyes are prominent. The antennulas (pi. VII, 

 fig. 39 ) surpass the middle of the third antennal segment. The first 

 segment of the antennas (pi. VII, fig. 39 b) is very short ; the terminal 

 segment is bristly hairy toward the apex. The external lamella of the 

 maxillipeds (pi. VII, fig. 41 a) is ernarginate on the outer side toward 

 the apex. 



The thoracic segments each bear a prominent median tubercle near 

 their posterior margins, and the first bears also a smaller tubercle near 

 its anterior margin. In the first two segments the posterior external 

 angles are salient and much elevated. The angulated epimera are evi- 

 dent from above in front of these projections. In the third and fourth 

 segments both lateral angles are salient but not elevated. In the last 

 three segments, only the anterior angles are produced, but the epimera 

 fill the places of the posterior angles. This arrangement gives the 

 appearance of fourteen teeth upon each side of the thorax, and the 

 prominent divergent tooth on the pleon makes, in all, fifteen. 



The operculum (pi. VII, fig. 39 d) is a little more vaulted than in the 

 next species and shorter ; the basal plate is less than three times as long 

 as broad; the terminal plate is triangular. The stylet on the second 

 pair of pleopods in the male (pi. VII, fig. 41 &, s) is slightly curved, 

 finely spinulose near the apex on the side toward the lamella, and 

 minutely and sharply denticulate on the opposite side at the apex, 

 as shown in the enlarged figure (s') of the distal portion of the stylet. 



Length ll mm ; breadth 3.4 mm . The color is a usually dull neutral tint 

 without bright markings, but sometimes more or less variegated with 

 brown or reddish, fading in alcohol. 



