560 NEW SPECIES OF PARASITIC COPEPODS. 



short, semicircular in outline, the rami very long, slender, and slightly 

 curved. Most of the remaining appendages are also relatively more 

 slender in the new species than in caiiddtus, but the long distal joint of 

 the i)Osteri()rantenniB is stouter in the former. (Compare Fig. 2 with Fig. 

 4, on Plate XXIX.) Entire length of the female, without the egg-tubes, 

 0.5 millimeters. European specimens of caudatus, in the collection of 

 the National Museum, average about 8 millimeters in length. 



Perissopua communis Kathbuu, new species. 

 (Plate XXIX, Figs. G,7; Plate XXX, Figs. l-C.) 



This species is closely related to Perissopus dentatus Sin. & Ltk. Be- 

 sides the typical form I have recognized one variety, called iStimp-soni, 

 which (litters from it almost exclusively in the characteis of the dorsal 

 surface. The typical form has been taken from four species of lish, and 

 ranges from Massachusetts to Florida, while the variety is re[)reseuted 

 by a single specimen, the host of which is unknown, collected many 

 years ago at Great Egg Harbor, New Jersey, by Dr. William Stimpson. 

 Only the female of both forms is known. 



Typical form.— Thm form is distinguished from P. dentaUis by its 

 proportionally longer and narrower body, less strongly produced pos- 

 tero lateral.anglcs of the cej^halothorax, the shape of the dorsal plates 

 of the second body segment, the narrower and deeper indentation of 

 the posterior margin of the iifth segment, and the characters of the 

 swimming feet, especially the third pair. The cephalothorax is semi- 

 elliptical in outline, very slightly wider than long, the lateral margins 

 nearly straight or gently convex, and very gradually divergent, the great- 

 est width being at or near the posterior angles, which are only slightly 

 )>roduced and appear angular from above instead of long and well- 

 lounded. The posterior margin is straight or very slightly concave, 

 with sometimes a minute spine on either side. The anterolateral an- 

 gles are regularly curved, and the anterior margin is considerably pro- 

 duced, in a broad frontal process, sinuous along the front, with a slight 

 indentation near the middle, the free extremities at the sides being 

 rounded and cut ott" somewhat obliquely inward. The dorsal plates of 

 the second, third, and fourth body segments are variable in shai)e, but 

 those of the second segment have always a very slightly oblicpie i)osi- 

 tion, with the outer margin gently convex or nearly straight, and ex- 

 posed for its entire length, while those of the fourth segment are only 

 very slightly exposed at the sides. 



The fifth segment is generally slightly wider than the cephalothorax, 

 and about three-fourths as long as wide, the greatest width being near 

 the middle. The sides are gently and regularly convex throughout 

 their entire length, and the posterolateral angles are each produced in 

 the shai)e of a small, slender, acute spine, which, in some of the s[K'ci- 

 mens, is more or less worn away. The posterior margin forms a mod- 



