31G DESCRIPTIONS OF PARASITIC COPEPODA. 



dorsal lobes of the secoucl segment elougate-oval, about twice as long 

 as broad; median portion with a transverse, subtriaugular, lobed plate, 

 as shown in the figure. Dorsal aj)pendage of the third segment divided 

 into two small, equal, and regularly curved lobes, the margins of which 

 meet, but do not coalesce, at the posterior extremity of the preceding 

 segment. Dorsal a[)pendage of tbe fourth segment very large and con- 

 cealing the greater part of tbe fifth segment ; width slightly greater 

 than twice the length ; median sinus subtriaugular in outline, the lat- 

 eral lobes formed by it semicircular in outline. Fifth segment very 

 short, as seen from above, and much narrower than the preceding seg- 

 ment; sides strongly and regularly curved, aud terminating posteriorly 

 in a small but prominent knob on each side of the median sinus, which 

 is broad, rounded, and of moderate depth. 



Caudal plate rather large, subcircular in outline, narrowing abruptly 

 anteriorly, about two-thirds in length projecting back of the fifth seg- 

 ment. Caudal stylets mostly uucovered from abosx, moderately loug 

 and narrow, thick vertically, and tertninatiug in three spiues arranged 

 vertically aud serially, as in P. siituatus. A wing-like projection ex- 

 tends inward from the anterior half of each stylet, and overlaps the 

 ventral caudal plate on the lower side. 



The sucking disks of the two anterior pairs, on the ventral side of the 

 first segment, are of about the same width and parallel ; outer oues 

 elongate-suboval in outline, inner about half as loug as the outer, aud 

 cut off sciuarely at the iront end. Rami of the posterior pair of feet 

 much longer and more slender than in P. Cranchii, aud also somewhat 

 more elongate than in even extreme cases of P. sinuatus; outer ramus 

 with five terminal spiues and one median spine on the outer margin, 

 situated in the middle of a rounded notch. 



The dorsal surface of the body is smooth and almost entirely of a rich 

 brownish black, the margins of the segments and the frontal plates being 

 lighter and of an amber or horn color. On the anterior portion of the 

 first segment there is also a transverse curved area of the same light 

 color. The fifth segment is blackish about the posterior knobs and 

 lighter anteriorly; the caudal plate is a deep rich brown, almost black. 



The above description is made up from two specimens taken from a 

 dusky shark, Carcharinus obscurus (Lesueur) Jor. & Gilb., caught otf 

 Noank, Conn., in 1874, by the U. S. Fish Commission (GiDS), aud the 

 drawings are from one of the same. The same species has also been 

 found on a specimen of sand-sliark, Odontaspin iittoralis (xMitch.) Jor. & 

 Gilb., taken in Vineyard Sound, Mass., by the Fish Commission, in 188U 

 (G022), aud on an undetermined species of shark from about the same 

 region (8119). There is only a single specimen in the lot numbered 

 8119. It measures 8'"°^ in length, and differs but slightly from the types 

 described above. The terminal knobs of the fifth segment are each 

 armed with a minute spine; the caudal plate is more elongate, being 

 oval in outline ; and the shaft of the caudal stylets is relatively broader, 



