REPORT ON THE COPEPODA. 47 



its first joint deeply excavated at the base, the lower border of the sinus forming at its 

 outer angle a strong curved spine. The outer branch of the third pair of feet in both 

 sexes has the basal joint produced externally into a stout thumb-like prominence (fig. 7), 

 and the two following joints have deeply sinuated margins, bordered with chitinous plates. 

 The fifth pair of feet in the male (fig. 8) is strongly prehensile, each branch ending in a 

 broad, clumsy, claw-like joint. In the female (fig. 10) each limb is simple, three-jointed, 

 the last joint bearing three long, subequal apical setae. The first segment of the female 

 abdomen (fig. 1) is tumid, and equal in length to the two following segments; in the male 

 (fig. 13) the abdominal somites are all of nearly equal length and shorter than broad, the 

 last somite in both sexes dilated at the distal extremity and forming two angular lateral 

 processes. The caudal laminae are about twice as long as broad, the setae subequal and 

 rather shorter than the abdomen. In some adult males (fig. 12), the abdomen is distorted, 

 bearing beard-like bunches of hairs or fimbriated marginal processes: in these specimens 

 the caudal laminae are also twisted and strongly setiferous. The pleural eye consists of a 

 strongly pigmented ring, covered by a highly refracting lens, the whole appearing to be 

 loosely attached just beneath the integument, and situated near the base of one of the 

 foot-jaws. The vulva forms a prominent black, conical papilla on the front of the first 

 abdominal somite. 



The description given above applies to specimens which I believe to represent the 

 completely developed adult form of the species : — these are figured in PI. XL A less 

 fully developed form, which appears to me to belong to the same species, and which is 

 undoubtedly identical with Pleuromma gracile, Claus, is shown in PI. XII. and PI. XXXI. 

 figs. 13, 14. The chief points of difference are to be found in the length of the abdominal 

 somites (figs. 14, 15), in the double hook of the first pair of feet (fig. 8), in the absence of 

 the two hooked spines of the female antenna (PI. XXXI. fig. 13), and in the want of a den- 

 ticulated plate in the male antenna; the fifth pair of feet in the male (PI. XII. figs. 10, 11) 

 are of somewhat different shape, and in the female (fig. 12) have only two, instead of 

 three, joints. In a still earlier stage of development (fig. 13), the branches of the female 

 fifth foot end in three straight spines, like the prongs of a fork. A similar condition is 

 shown in PI. XL fig. 11, drawn from specimens taken along with the adult form 

 figured in the same plate. Fig. 9 in PL XL represents what I believe to be an 

 immature form of the fifth foot of the male. In some males of the immature form the 

 antennae bear numerous very largely developed sensory organs, club-shaped or pyriform 

 (PI. XII. fig. 2). These are sometimes so numerous and so closely packed that I at first 

 doubted whether they were not parasitic growths ; this, however, is certainly not the case. 

 But the most important distinction between the normal form of the species and the Pleu- 

 romma gracile of Claus is that, in the former the right male antenna is the geniculated one, 

 in gracile the left. This is a difference which I cannot yet satisfactorily explain. But 

 considering the variable situation of the pleural eye, and the very fluctuating characters 



