ABT. 18 NEW COMMERCIAL COPEPODS SEIWELL 3 



Genus TISBE Lilljeborg 1853 (IDYA, Philippi, 1843, preoccupied) 



Generic characters. — Body distinctly depressed, with the anterior 

 and posterior divisions sharply defined. Cephalic segment of mod- 

 erate size, narrowly produced in front, rostral projection short and 

 obtuse, not defined at the base. Epimeral plates of the three succeed- 

 ing segments, rather broad, lamellar, obtuse at the tips. Last seg- 

 ment of metasome very small. Urosome moderately slender, with 

 the genital segment in female distinctly divided in the center. Geni- 

 tal tubercles in male each armed with a strong, posteriorly pointing 

 spine. Caudal rami generally short but with some of the apical 

 setae much elongated. Eye normal. Anterior antennae slender and 

 attenuated, eight articulate, sensory filaments of fourth joint fully 

 developed; those of male slightly transformed, subprehensile. Pos- 

 terior antennae with the outer ramus well developed, four articulate. 

 Anterior lip prominent, tapering distally, terminal edge minutely 

 denticulate. Mandibles with the masticatory part rather slender 

 and coarsely dentated at the tip, palp of comparatively simple struc- 

 ture, though distinctly biramous. Maxillae with the palp slightly 

 lobular, epipodal lobe wholly absent. Both pairs of maxillipeds 

 uncinate at the tip, the anterior ones biarticulate, with a single 

 slender lateral lobe at the junction of the two joints, the posterior 

 ones distinctly three articulate, with a single apical claw. First pair 

 of legs with both rami three articulate, but rather unequal in size 

 and structure, the inner one much larger than the outer and having 

 the penultimate joint prolonged, the last very small with two com- 

 paratively short claws, outer ramus with the spine of the first joint, 

 as a rule, elongated, that of the second joint issuing from near the 

 end, last joint provided at the inner corner with two slender ciliated 

 setae, and along the obliquely truncated end with four outward 

 curving spines gradually increasing in length, and each like that of 

 the second joint, penicillate at the tip, or clothed on one edge with 

 a limited number of long cilia. Natatory legs comparatively well 

 developed, with the rami nearly equal and the joints broad subla- 

 mellar, middle joint of inner ramus in all pairs with two natatory 

 setae. Last pair of legs slender, extended laterally, proximal joint 

 very slightly expanded inside, distal joint generally narrow, linear, 

 those in male similar though somewhat smaller than in female. 



TISBE WILSONI, new species 



Specific characters — Advlt male (Holotype, Cat. No. 61142, 

 U.S.N.M.). — Body of male grayish white with a dark patch in the 

 epimeral plate on either side of the first four thoracic segments. The 

 first segment being fused with the head, its two patches appear near the 

 posterior margin of the cephalothorax. Eye visible. Body much 

 more slender and elongated than that of female, anterior and pos- 



