640 Brady and Norman — Monograph of the Marine and Freshwater Ostracoda 



in double file. In Crossophorus a similar organ is present in the two sexes (PI. liii., 

 fig. 2), but here it is densel}^ filiferous. In Philomedes the sensory organ is absent 

 in ? (PI. LVii., fig. 12), but similar in character to that of Crossophorus in the S 

 (PI. LVII., fig. 1). In Nematohamma S it consists of a very short clavate stem 

 (PI. LIII., fig. 12), the termination of which is closely beset with an immense 

 number of slender filaments of extraordinary length and great flexibility, and to 

 the clavate stem there also is attached a long, closely-annulated seta. The females 

 of Tetragonodon, Paramekodon, Sarsiella, and Ruiiderma, have no sensory appendage, 

 its usual place being occupied by either a simple, or an annulated seta. The 

 terminal setae of the limb in tlie ? are ringed, and three or more are usually 

 subequal in length. In <J they undergo for the most part various modification ; 

 in Nematohamma they are similar to those which usually occur in the other sex ; 

 and in Crossophorus there are also four long setai subequal in length ; but in the 

 genera Philomedes and Cypridina two setse are of excessive length, more especially 

 in Philomedes, in which genus these long setse are usually carried reflexed upon 

 the limb (PI. ll, fig. 4). In Cypridina a further peculiar modification takes place 

 (PI. LX., figs. 19-21), two setse, of much less length, are bulbously swollen at the 

 base, and bear a flattened spine-like process to the side of which are attached one 

 or two circular, saucer-like sucking disks ; moreover, the longer setse throw off 

 strap-formed processes from their side, some of which processes are also furnished 

 with sucking disks. 



The antennse (PI. LV., fig. 4) consist of a basal joint of prodigious size, and 

 one or two branches ; the great basal joint is subcordate or pyriform, its breadth 

 in some genera exceeding the length. To the end of this basal joint is attached 

 the well-developed swimming branch, which consists of nine joints, the first very 

 long, the remaining joints short, but the third in $ is often longer than the 

 second. Each joint from the second to the eighth is furnished with one long, 

 ringed, plumose swimming seta, but sometimes in the female the setse are shorter 

 than in the male, and sparingly setose; the last joint ends in 2-4 similar setse. 

 Springing from the end of the basal joint, below the origin of the swimming 

 branch, is usually in the female a second (appendicular) branch of much smaller 

 size, but this branch appears to be wholly absent in Rutiderma. In Paramekodon 

 it is represented by a very large, ringed, plumose seta, near the origin of which 

 are three very small, ringed setse. In Sarsiella and Tetragonodon it consists of 

 one minute papillary joint, bearing a seta. In Cypridina and Philomedes the 

 development is greater, the organ consisting of at least two small joints furnished 

 with setse. In the male this branch attains usually greater development (PI. lvil, 

 fig. 2), and assumes the form of a grasping organ, usually three-jointed, with the 

 last of these joints more or less curved or falcate, and capable of reflection on 

 the penultimate joint; but in the genus Cypridina it does not differ from that 



