THE COPEPOD GENUS PARANTHESSIUS — ILLG 425 



The maxilliped is developed to a degree remarkable among the mem- 

 bers of the genus. Here it is the most conspicuous of the mouth parts, 

 very considerably exceeding in its dimensions the maxilla, which is 

 usually the most prominent oral appendage. The basal segment is 

 long and is expanded basally in its complicated articulation with the 

 surface of the head. The exact proximal limit of the appendage could 

 not be made out. The second segment is the longest. It has rather 

 irregular contours with a slight injflation of outline toward its center. 

 A single minute seta is borne slightly distal to the center. The distal 

 segment is a short cone bearing at its apex a small, articulated hook. 

 It would be a matter of opinion to interpret the hook as a dactylar 

 segment or, alternatively, as a process of the usual 3- jointed appen- 

 dage (fig. 37, M). 



The swimming legs have the same distribution of spines and setae 

 as has been given above for P. columhiae. A most distinctive feature 

 of the first legs is the modification of the more proximal spines of 

 the exopodite. The spine of the first joint of this ramus is expanded 

 and flattened in the plane of the appendage and both margins consist 

 of rows of elongate, highly developed, secondary denticles (fig. 35, 

 L) . The spine of the second segment and the three more proximal 

 spines of the terminal segment all exhibit the same flattening. In 

 these spines, however, the pectinate denticles are restricted to the more 

 proximal margin (fig. 35, M). The distal margins of these spines 

 exhibit the coarsely serrated, almost transparent laminae that are 

 seen on the spines of all the species of Paranthessms considered here. 



The apical segment of the fourth endopodite bears terminally two 

 subequal spines. The medial spine exceeds the lateral one by about 

 one-sixth of its own length. Both spines are very stout (fig. 37, N). 



The fifth leg is peculiar to the species. The free segment is inflated 

 and larger basally than distally. At about one-third of the length of 

 the segment from the base there is a pronounced constriction. Of the 

 terminal outgrowths, the more anterior is the stouter and longer 

 (fig. 37,0). 



The abdominal somites exhibit no spinous ornamentation. The 

 caudal rami are about six times as long as wide (fig. 37, P). The 

 proximal lateral seta is inserted just midway on the lateral margin. 

 Of the four terminal setae, the more lateral is longer than the medial 

 seta. The two central setae are jointed basally. At the distal 

 extremity these two setae tend to curl into loose spirals. The longest 

 seta is about one and one-half times the length of the ramus. None of 

 the setae bears ciliation. The length of the body, exclusive of the 

 caudal setae, is 1.3 mm. 



No male was found. 



