408 PROCEEDESTGS OF THE NATIONAL MUSEUM vol. 99 



of the basipodites are of heavier, more spinulelike members, partic- 

 ularly in the first three legs. The fourth pair is more like that of the 

 female. A further feature of the first three legs is the prolongation 

 of the distal medial corner of the second segment of the endopodite 

 into a long, stout spinous process. This is not a true spine, as it lacks 

 an articulation at the base and is therefore a direct extension of the 

 integument of the podomere proper. These spinous processes are 

 equivalent in size to the true, articulated spines, however. The con- 

 trast between these structures in the male and female is illustrated 

 (fig. 36, C, F) for Paranthessim panopeae, the species in which the 

 dimorphism is seen most strikingly. In the original description of 

 Pseudolichomolgus pectinis Pesta, the illustrations show spines on the 

 two proximal segments of all the endopodites. If these were mov- 

 able spines, this would represent an unique condition among licho- 

 molgids. The illustrations do show a somewhat subtle differentiation 

 (;f these outgi'owths from the truly articulated spines in the usual 

 positions, and I suggest that they be interpreted as spinous processes 

 comparable to those seen in the males described here. 



The male fifth leg is reduced, much shorter in proportion to width 

 than in the female, and the outgrowths are less robust, more setiform 

 { fig, 34, H) . The lateral seta is longer than the medial. 



The seventh thoracic segment of the male is much modified because 

 of a pair of chambers containing the sperm masses. The ventral 

 portion of the segment is prolonged posteriorly on each side, and at 

 the lateral limit of this prolongation is the slight prominence bearing 

 two setae that constitutes the sixth leg. The posterior border of the 

 prolonged region is further ornamented by spinules set in row forma- 

 tion parallel to the margin. In the present species there are two 

 such rows of spinules on each side, parallel to each other, the count 

 of spinules for one side being 24 in the anterior row, 16 in the posterior 

 row. Figure 35, G, shows the arrangement of this segment and leg 

 for Paranthessius panopeae. 



The terminal abdominal segment bears the rows of spinules char- 

 acteristic of the species in both sexes, and there is no notable dimorph- 

 ism of the caudal rami. The body length is about 1.7 mm. 



Immature forms : The several specimens available of late develop- 

 mental stages at first presented a puzzling complex of resemblances and 

 differences. As will be presented in detail below, sufficient features 

 were established to conclude that a portion of these represented the 

 females and males of the final larval stadium (the fifth copepodid) 

 and the remainder were of the fourth copepodid stage, in which no 

 basis for differentiation of the sexes was discovered in the small sample 

 considered. 



