124 MESSES. NOEMAN AND STEBBIKG ON THE 



2. Anthuea tenuis (Harger). 

 1878. Ptilanthura tenuis, Harger, Amer. Journ. Sci. ser. 3, vol. xv. p. 377; Proc. Unit. Stat. Nat. 

 Mils. 1879, vol. ii. p. 162; Report Unit. Stat. Commis. Fish and Fisheries, pt. vi. for 1878 

 (pubUshed 1881), p. 406, pi. xi. fig. 71, a-e. 



It is probable that the male of Anthura gracilis which we have just described and 

 figured is the immature animal, and that, after the exuviation which should bring it to 

 its perfect state, the upper antennae would have a plumose flagellum. If that supposi- 

 tion be correct, then it would bear a great resemblance to Harger's figure oi Ptilanthura 

 tenuis ; moreover, A. gracilis has slight depressions on the back of the segments, as 

 described and figured by Harger, and, although that author does not mention the keeled 

 character of the margins of the perseon-segments, it seems to be shown in the figure. 

 But, notwithstanding these resemblances, A. tenuis is clearly distinguished by the 

 form of the telson, which is described as " about as long as preceding five segments, 

 elongate-ovate and obtusely pointed behind." Mr. Harger's description of the palp 

 of the mandible being of only one joint is probably a mistake ; the palp might easily 

 have been damaged in dissection and produced a false impression. 



Genus 2. Ctathura. 



Ctathuea cakinata (Kroyer). (Plate XXVII. fig. in.) 

 1844. ? Anthura gracilis, Dekay, Zool. New York. Crust, p. 44, pi. ix. fig. 34 (but not A. gracilis, 



Montagu) . 

 1847. Anthura carinata, Kr63'er, Naturhist. Tidssk. 2 ser. ii. p. 403, and Voyage en Scand. 



pi, xxvii. fig. 3; Schiodte, Krebs. Sugem., Naturh. Tidssk. 3 ser. x. p. 211, pi. iv. figs. 1-14, 



and Ann. Nat. Hist. 4 ser. .wiii. (1876) p. 253; Meinert, Crust. Amphip. et Decap. Danise, 



Naturhist. Tidss. 3 ser. xi. (1877) p. 77, and xii. (1880) p. 470. 

 1856. Anthura polita, Stimpson, Proc. Acad. Nat. Sci. Phil. vol. vii. p. 393 ; Harger, Proc. Unit. 



Stat. Nat. Mus. 1879, vol. ii. p. 162 ; Harger, Report Marine Isopoda of New England &c., 



Rep. Unit. Stat. Comm. Fish and Fisheries, pt. vi. for 1878, p. 398, pi. xi. figs. 68, 69. 

 1874. Anthura brunnea, Harger, Rep. Unit. Stat. Comm. Fish and Fisheries, pt. 1, p. 572 (278) j 



Verrill, 1. c. pt. 1, p. 426 (132). 



Body of uniform width throughout. Head broader than long, with slight central 

 and lateral projections in front. 



Perseon : first segment the longest ; second to fifth subequal to each other, and 

 scarcely longer than broad, and of equal breadth throughout ; sixth and seventh equal 

 to each other, and rather shorter than the preceding. The perseon is keeled below, 

 and the third to the fifth segments have a slight pit on the anterior part of their dorsal 

 surface. 



Pleon with the five first segments, in the female at any rate, completely coalesced 

 into a single segment, which is equal to the last of the pereeon in length ; sixth segment 

 very minute. 



