348 PnOCEEtolNGS of the national MV8EVM. VOL. XXXIII. 



In Perissopus there are three free thorax joints, each carrying a 

 pair of dorsal plates, of wliich the first pair is lateral, the second 

 median, while the third extends entirely across the body; the geni- 

 tal segment is squarely truncated posteriorly, with sharp spines at 

 the corners; the second antennae are short, with a small terminal 

 claw; all four pairs of s%vimming legs are biramose, with enlarged and 

 lamellar basal joints; rami of the third and fourth pairs minute and 

 rudimentary, the exopod diifering from the endopod, and the third 

 pair from the fourth pair. 



In Pholidopus, on the contrary, the second and third thorax seg- 

 ments are fused together, and carry but a single pair of dorsal plates, 

 which are like those on the fourth segment, extending entirely across 

 the body; the genital segment is incised at the center posteriorly, 

 each side being evenly rounded in a semicircle, without any spines; 

 the second antenna? have short basal joints, Math a very long sickle- 

 shaped terminal claw, set with two rows of teeth; the first pair of 

 legs is uniramose and three-jointed, the other pairs are biramose; but 

 the basal joints of the first two pairs are narrow and slender, not 

 lamellar; the last two pairs have lamellar basal joints, but all of their 

 rami are just alike and armed ^\'ith spines at their tips. 



Genus LEPIMACRUS Hesse. 



Lepimacrus jourdaini Hesse, 1883, p. 6, pi. iv, figs. 8-17. 



Hesse described, in the above reference, a new genus and species 

 based upon a single female specimen obtained from LaTnna cornubica. 

 The species has never been seen by any other writer, so that Hesse's 

 description is all the knowledge we have of it. And although this 

 description is faulty and the figures give us few reliable details, yet 

 enough is shown to determine with reasonable certainty that the speci- 

 men really represented a new genus. Consequently it is here included 

 and is differentiated as well as possible from the other genera in 

 the following diagnosis. 



Female. — Carapace elliptical, rather pointed anteriorly, the sides 

 slightly emarginate; frontal plates prominent; eyes small and close 

 together. Four pairs of dorsal plates on the thorax 'segments, first 

 and third pairs median, second and fourth pairs lateral. First two 

 pairs subquadrangular; first pair fused at the base but separated for 

 most of their length by a broad sinus ; second pair widely separated, 

 even at their bases. Last two pairs narrow and elongate; third pair 

 separated at their bases but meeting at their tips on the midline; 

 fourth pair on the genital segment, each plate semilunar, the convex 

 sides toward each other and fused for some distance at the center. 

 The tips of these plates are divergent; they project far behind the 

 genital segment and are armed ^\dth stout spines; abdomen small, one- 



