478 



BULLrETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Genus DICHELESTHIUM Hermann, 1804 



Female. — Head fused with first segment, strongly narrowed an- 

 teriorly; second and third segments produced laterally into short 

 lobes, and with these lobes as wide as the carapace; fourth and 

 fifth segments narrower and longer, tapered posteriorly, without 

 lateral lobes ; genital segment still narrower and longer, and tapered. 

 Abdomen 1-segmented, attached to the ventral surface of the genital 

 segment; caudal rami small and foliaceous. First antenna 8-seg- 

 mented; second antenna cheliform; maxillipeds uncinate; first two 

 pairs of legs biramose, rami 1-segmented (two segments fused) ; 

 third legs uniramose, 1-segmented ; fourth and fifth legs wanting. 



Male. — Smaller than the female, head relatively larger, genital 

 segment considerably shorter; no transverse grooves on the thoracic 

 segments. Endopod of second leg very short and wide; third legs 

 each a 1-segmented lamina wider than long, with a lobe at the end 

 suggesting a second segment. A single species known. 



DICHELESTHIUM OBLONGUM (Abildgaard) 



Figure 286, a 



Caligus otlongus Abildgaard, Skrivt. Naturh. Selsk., vol. 3, p. 52, 1794. 

 Dichelesthium oblongum T. and A. Scott, The Britisli parasitic Copedoda, p. 106, 

 pi. 31, figs. 7-18, pi. 45, figs. 4-5, 1913. 



Occurrence. — Found in abundance on the gills of the sturgeon 

 (Acipenser sturio) everywhere in the Woods Hole area. 



FiGDEB 286. — a. Dichelesthium ohlongum, female, dorsal (drawn by J. H. 

 Blake, 1874) ; 6, Peniculus clavatus, female, lateral; c, P. clavatus, first 

 and second antennae 



Distribution. — Rhine at Strassburg (Hermann, Desmarest) ; riv- 

 ers of northern Europe (Latreille, Nordmann, Burmeister) ; British 

 Isles (T. and A. Scott) ; Woods Hole, Vineyard Sound, Long Island 

 Sound (Rathbun, Wilson). 



