330 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 39. 



Mouth-parts large and distinctly defined; the terminal joints of the 

 mandibles very wide and fringed with long hairs, the basal joints 

 large and muscular. The palps are rather narrow, but are fringed 

 with long hairs like the mandible itself. First maxillae in the form of 

 large and nearly spherical knobs, each armed with two setae. 



Second maxillae with large and triangular basal joints, which 

 extend outward nearly to the lateral margin, and forward in front of 

 all the other mouth-parts. The terminal joints are also large and 

 stout and are heavily fringed along their anterior margin. 



In the swimming legs the endopod of each pair is larger than the 

 exopod; both rami are three-jointed, except the exopods of the 

 fourth legs, which have but a single joint. 



The fifth legs are reduced to small spines nearly invisible. 



The arrangement of the spines and setae on the first four pairs of 

 legs is as follows: First exopod, I-O; 0-1; II-6: endopod, 0-1; 

 0-1; II-3: second exopod, I-O; 0-1; 0-6: endopod, 0-1; 0-2; II-4: 

 third exopod, I-O; 0-1; 1-5: endopod, 0-1; 0-2; II-5: fourth exo- 

 pod, 1-4: endopod, 0-1; 0-2; 1-3. 



Color in sexually mature specimens a uniform milk-white on the 

 dorsal surface; in other individuals with a bluish tinge and trans- 

 lucent, but always with a variegated pattern of blue pigment along 

 the center of the ventral surface on either side of the mid-line (fig. 43). 



Total length, 1 to 1.25 mm. Length of carapace, 0.65 mm. 

 Width of same, 0.5 mm. Length of free segments, 0.17 mm. Length 

 of egg-strings, 0.95 mm. 



(lahracis, from Ldbrax, the generic name of its host.) 



This species was first found by Kroyer in considerable numbers on 

 the gills of the striped bass, Roccus lineatus (Lahrax lineatus Kroyer) 

 at Baltimore, Maryland, in the year 1860. It was afterwards (1887) 

 found by Leidy to be common on the gills of the same fish in the 

 Philadelphia markets, but he added nothing in the way of descrip- 

 tion to what Kroyer had given. 



The first description and drawings, therefore, are the only ones that 

 have ever been given, and it is hoped that the present account will 

 supplement this in many ways. 



The National Museum collection contains four bottles of speci- 

 mens obtained at different times by Dr. H. M. Smith, of the U. S. 

 Bureau of Fisheries, from the gills of the same striped bass in the fish 

 markets at Washington, District of Columbia. These bottles are 

 numbered respectively 38633, 38653, 38654, and 38657. 



The first and the last of these contain the gills themselves, with the 

 parasites still clinging to the filaments, and are very instructive in 

 showing how thoroughly our food fish may become infested with 

 these creatures. Beside these there are two bottles, numbered 

 38655 and 38656, which also contain infested gills of striped bass 



