388 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



( Tsenia, a genus of tapeworms, and aKavOa, a spine, the maxillary 

 hooks being similar to the hooks on the rostellum of Tsenia) . 

 Type-species. — Tseniacanthus carcharise Sumpf. 



ARTIFICIAL KEY TO THE SPECIES. 



a. Free segments diminishing regularly in size; fourth segment but little wider than 

 the fifth albidus, new species, p. 388. 



a. Second, third, and fourth segments fully as wide as the carapace; fifth segment 

 abruptly narrowed to one-third that width carcharise Sumpf, 1871. 



T.ffiNIACANTHUS ALBIDUS, new species. 



Plate 60, text fig. 41. 



Female. — First thorax segment fused with the head; resultant 

 cephalothorax semielliptical, one-half wider than long, with a slight 

 incision between the antennae and a squarely truncated posterior mar- 

 gin. Second and third thorax segments the same length and mdth, 

 four-fifths as wide as the carapace. Fourth segment the same length 

 but one-third narrower; fifth segment half as long and three-quarters 

 as wide. Genital segment trapezoidal in outline, with romided cor- 

 ners, the same width as the fiith segment and twice as long, widest at 

 the anterior margin and tapering posteriorly. The genital orifices 

 are on the upper surface of the segment and close to the anterior mar- 

 gin. Abdomen three-fourths as wide as the genital segment and 

 four-jointed, the first two joints somewhat longer than the last two. 

 Anal laminae narrow and widely divergent, two-thirds as long as the 

 last joint, and each tipped with two setae, of which the inner is two 

 and a half times the length of the outer; there is also a short spine 

 on the outer margin of each lamina near the center. Egg-cases of 

 good size, tapered at each end, half the entire length and as wide as 

 the genital segment. Eggs minute, arranged in fifteen or more longi- 

 tudinal rows, about four hundred in each case. 



First antenna presumably six-jointed, the three terminal joints 

 distinct, the three basal ones thoroughly fused. This basal portion 

 of the antenna is enlarged and turned outward at a right angle, as in 

 Bomoloclius. It carries along its anterior border a row of flattened 

 plumose setse, all of which are the same size and structure, and there 

 are no tactile hairs or spines among them. The terminal joints are 

 also well supplied with setae, of which one at the distal end of the 

 fourth joint is much larger than the others. 



The second antennae are three-jointed, the basal joint as long as 

 the other two and serving for the attachment of the appendage, the 

 second and third joints the same length and folded back against the 

 basal joint. The ventral and posterior surfaces of these last two joints 

 are roughened with rows of short spines, and the last joint terminates 



