no. 1404. PARASITIC COPEPODS—CALKHDE— WILSON. 581 



carapace. They taper forward to a sharp point at the base of the 

 frontal filament as though pulled out by the latter. The two terminal 

 joints of the first antenna are attached to the posterior border of the 

 frontal plates, giving them the appearance of being- attached to the 

 lateral margin of the carapace, well back toward its center (fig. 114). 



The eyes are so far back as to be a little behind the apparent center, 

 though they are not far from the actual anterior margin of the cara- 

 pace. There are no posterior sinuses, the third thorax segment not 

 having yet fused with the head. This leaves the posterior margin of 

 the carapace concave, the posterior corners projecting somewhat. The 

 third thorax segment is separated by a well-defined groove from the 

 carapace; it is a little wider, but only half as long as the fourth seg- 

 ment, and from its well-rounded sides project the third swimming legs. 



The latter have not yet acquired their broad basal apron, but are 

 almost exactly like the second pair, and the exopods can be plainly 

 seen in dorsal view. The fourth segment is long and large, with well- 

 rounded sides; the fourth legs are attached near its posterior margin 

 and are quite rudimentary. 



The genital segment and abdomen are still fused, though the line of 

 separation is indicated by a deep indentation on either side. 



The anal lamina? are small but the plumose seta? are long and stout. 



The total length of the earliest stages is only a trifle over 2 milli- 

 meters, of which the carapace, including the frontal plate, makes: up 

 about four-sevenths. 



This species occurs very frequently and often in great abundance 

 upon the codfish of our coast, but has been rarely observed on other 

 species of fish. Most of the specimens in the collection of the National 

 Museum agree closety with the Caligus americanus, so well described 

 by Pickering and Dana (1838). 



Hut there are a few lots of females in which the abdomen is broader 

 and more nearly quadrangular. A careful examination of these 

 specimens, however, fails to reveal the slightest differences in the 

 appendages and hence they can not be regarded as even a variet}". 

 This is one of the species upon which Midler founded the genus 

 < 'aligns in L785, and is the only one of the types which has proved to 

 be a real Caligus, the others belonging to other genera. Hence the 

 present species is left as the sole type of the genus. 



Many lots of specimens have been obtained by the United States 

 Fish Commission from codfish taken along the New England coast 

 from Maine to New York, and on the offshore fishing banks. They 

 are exceedingly abundant during the autumn of the year when the 

 shoal-water fish are brought into the local markets, and they gradually 

 diminish as the season advances. They are most numerous on half- 

 grown fish and may be found anywhere upon the externa] surface or 

 the lias. They are also rarely taken in company with ('. rapaxinthe 



