On a Parasitic Copepod from Cephalodiscus. 179 



prominence bearing a single terminal seta (fig. 4, mx"). A com- 

 parison with Enterognathus suggests that these prominences probably 

 represent the second maxillae. No other mouth-parts appear to be 

 present. 



The first four pairs of thoracic feet (figs. 7 and 8) are similar in 

 form. The protopodite is more or less distinctly divided into two 

 segments, of which the distal bears externally, in the first three 

 pairs, a fine seta. The basal part of the exopodite is not distinctly 

 defined from the protopodite ; it has, on the inner edge, a minute 

 seta which is largest in the third pair and seems to be absent from 

 the fourth. Distally, the exopodite ends in a sickle-shaped claw, 

 at the base of which a small segment can in some cases be detected. 

 The endopodite is apparently unsegmented, and forms a broadly 

 ovate or nearly circular leaflet, bearing four small blunt papillae on 

 its distal edge. 



The feet of the fifth pair (fig. 6) are large ovate plates attached 

 to the side of the body and pointing backwards. Two very minute 

 setae were observed on the distal margin of each. 



Male in Fifth Copepodid Stage. 



(Plate XIX.) 



Total length, -6 mm. 



The general shape is CyclojJS -like, rather elongated, the greatest 

 breadth being about J of the length. The fifth thoracic somite 

 is distinctly narrower than the fourth. The head is about J of the 

 total length, bluntly pointed in front, with a deflexed rostrum 

 as in the female. The pleura of the head-region are not bent 

 inwards as they are in the adult male of Enterognathus. The first 

 three somites of the abdomen (fig. 14) diminish successively in 

 length ; the fourth is as long as the first, and beneath the cuticle 

 can be seen the division between the fourth and fifth somites of the 

 adult. On the ventral surface of the genital segment are the genital 

 valves (fig. 14, g.v.), each truncate posteriorly and bearing two setae. 

 The furcal rami are longer than in the female and each bears six 

 spines ; the inner spine is set on the dorsal surface, the outer one 

 is minute, and the terminal four, of which the second is the largest, 

 are stout and strongly curved outwards. 



The antennules (fig. 12, a') have a very delicate external cuticle 

 which does not seem to show any segmentation proper to this stage, 

 but within which can be seen, in the specimen examined, the seven 

 segments of the succeeding (adult) stage. They are beset with 

 fairly numerous simple hairs but no aesthetascs were observed. The 



