6 PROCEEDINGS OF THE NATIONAL MUSEUM, vol.60 



Lernanthropus and Hatschekia are cosmopolitan, using a great 

 variety of fish from every ocean and nearly every latitude ; Congeri- 

 cola is found on the Labridae, or wrasse fishes, chiefly in the Medi- 

 terranean; most of the other genera are made up of single species 

 widely scattered. 



Being found chiefly upon nonedible fishes, the species of this 

 family have but little economic importance, and in addition they 

 are of such small size and occur in such limited numbers that their 

 importance is still further restricted. In most families of parasitic 

 copepods the number of specimens upon a single host may be in- 

 creased under favorable conditions until it becomes a menace to the 

 life of the fish. Nothing of the sort has ever been reported in 

 connection with the present family. 



Food. — The presence of the great majority of the species upon 

 the gills of their hosts and the color of the contents of the digestive 

 tube when freshly examined leave no doubt that these parasites eat 

 the blood of their host. The walls of the stomach also have the 

 same structure as those of other blood eaters. That the amount con- 

 sumed by a single parasite is small may be inferred from the fact 

 that it is content to remain upon the gills, in company with other 

 kinds of parasites, instead of boring into the flesh to get at some 

 large blood vessel. 



MORPHOLOGY. 



GeTieral hody form. — In general the body of a dichelesthiid is 

 elongate and tapers gradually from the head to the abdomen. The 

 thorax is usually distinctly segmented and the genital segment is but 

 little wider and longer than the preceding segment, but in the genera 

 Pseudocycnus, Gongericola and Kr0yeria the genital segment is 

 greatly elongated and is considerably wider than the free segments. 

 In the genus Lernanthropus there is considerable fusion of the 

 thoracic segments, and the body is greatly modified by the trans- 

 formation of the posterior swimming legs into soft laminae, nearly 

 as long as the body itself. In Pseudocycnus and Hatschekia only 

 two of the anterior thoracic segments are free, the posterior segments 

 being fused with the genital segment to form a body region much 

 longer than the cephalothorax. Another factor which profoundly 

 modifies the general body form is the presence of dorsal plates, or 

 wings, or both. In Lernanthropus the dorsal plate which covers 

 the posterior thorax and abdomen is sometimes elongated and 

 widened so much, and is wrapped around the body in such a way, as 

 to give the body the appearance of being clothed in a skirt. 



In Sagum the dorsal plate is prolonged at the posterior corners 

 into large lobes, which have the appearance of a military cloak 

 draped around the body. In Norton the dorsal plate is prolonged 



