360 BULLETIN OF THE BUREAU OP FISHERIES. 



teeth. First tnaxillse small but protruding well and armed with long setae; second maxillae with a 

 broadly triangular blade, fringed ouly along its posterior margin; muscles and rudiments of the maxilli- 

 peds present behind the second raaxillas; lower lip a small narrow, semicircular plate behind the tips of 

 the second maxillae. Endopodofthe first swimming legs and exopod of the fourth legs two- jointed ; all 

 theother rami three-jointed; arrangement of the spines and setae as follows: First exopod, i-o, o-i, n-5; 

 endopod, o-i, 11-5; second exopod, i-o, o-i, 1-6; endopod, o-i, 0-2, 1-4; third exopod, 1-0,0-1,1-5; 

 endopod, o-i, 0-2, 1-4; fourth exopod, l-o, 1-5; endopod, o-i, 0-2, 1-3. 



Ground color that of transparent cartilage, covered over the entire ventral surface with large irregular 

 patches of deep purplish blue; these coalesce into a line along either side of the digestive tract, which 

 latter is a rich golden yellow; on the bases of the antennae and mouth parts, aroimd the eyes, and out- 

 side the blue line in the genital segment are patches of pale brick red; the compound eye is dark purple. 



Totallength, 1.25mm.; cephalothorax, 0.60 mm. long, 0.40 mm. wide. Egg strings, 0.50 mm. long. 



(elegans, elegant, neat in appearance.) 



Remarks. — This species closely resembles versicolor, but can be readily distinguished by the two- 

 jointed endojxjd of the first legs. From all the other species it is at once distinguished by its varied 

 coloration, as well as by its free-swimming habits. It is associated with Lampsilis anodonioides , the 

 yellow sand-shell, and apparently with no other glochidia. Accordingly it is likely to be found upon 

 the alligator gar at the right season. 



In swimming the large second antennae are folded like arms across the thorax, and neither they nor 

 the first antennae are used for locomotion. 



Movement is accomplished entirely by means of the swimming legs and consists of a series of rapid 

 dashes, without any particular direction. 



These movements are swifter and they carry the copepod many times farther tlian those of the 

 regular free-swimmers, so that if tlie tow be placed in a large shallow glass these free-swimming parasites 

 can be at once detected by their movements. Apparently this species swims about freely in the slews 

 until its eggs are ripe, since the females obtained from the tow are fully as large as those from the fish. 



Like the young Arguli they frequent the surface in the daytime and sink to lower depths at night, 

 and they must fasten upon the fish when fully matured rather than in a larval stage. 



Ergasilus cseruleus Wilson. (PI. lxix, fig. 74.) 



Ergasitus cceruteiis Wilson. Proc. U. S. Nat. Mus., vol. 39, p. 334, pi. 43. 



Host and record of specimens. — When this species was established it was found only upon bluegills 

 in Tippecanoe Lake and Twin Lakes, Ind. Here in the Mississippi River, however, it is extremely 

 abundant; its chief hosts are the two crappies, Pomoxis annularis and P. sparoides. 



From the former lots have been obtained which have received catalogue no. 43531, 43535, 43530, 

 43532, U. S. National Museum; from the latter the lots are catalogue no. 43545, 43514, U. S. National 

 Museum. Catalogue no. 43541, U. S. National Museum, contains a set of gills just as they were taken 

 from P. annularis, with the parasites preserved in sitii, and nearly 500 of them upon the single fish. 



A single female (catalogue no. 43538, U. S. National Museum) was obtained from the blue-spotted 

 sunfish, Apomoiis cyanellus; several (catalogue no. 47774, U. S. National Museum) were taken from tlie 

 bluegill, Eupomoiis gibbosus, captured near Fairport , Iowa ; two were found on the sauger, Stizosiedioii 

 canadense (catalogue no. 47776, U. S. National Museum); three on thegillsof the white bass, Roccuschry- 

 sops (catalogue no. 47777, U. S. National Museum); and one on the gills of the long-nosed gar, L. osseus. 

 These fish were all captured in the Mississippi River at or near Fairport during the present season. 



Newly hatched nauplius larva. — Some of the females obtained on August 14 were carr>'ing eggs whose 

 blue color showed that they were ready to hatch. These were accordingly placed in a suitable aquarium 

 and all hatched out on the following day. The issuing nauplius proved to be quite similar to that of 

 Ergasilus centrarchidarum, but with these differences: 



General body form ovate, considerably narrowed and pointed posteriorly, and nearly twice as long 

 as wide; the knob at the posterior end, the future abdomen, is much larger than in centrarchidarum and 

 projects farther. The three pairs of appendages are similar in all their general features to those of the 

 other Ergasilidae and differ only in little details. The basal joint of the first pair is somewhat swollen; 

 the masticatory process on the second pair is proportionally large and carries a very long spine which 

 is not much ciu-ved; the lamina shaped like the blade of a case knife, found upon the endopod of the 

 third appendages, is sometimes jointed and is relatively large. 



