198 CEYLON PEARL OYSTER REPORT. 



legs plainly at their tips. The abdomen has elongated and its sides are now 

 parallel. 



The appendages have assumed their final form, and the rami of the swimming legs 

 have all become clearly three -jointed. 



About ten specimens of this species were obtained from Rhinoptera javanica, 

 including the two stages of early development. The species is of peculiar interest, 

 because it is the only one besides KROYER'S original type (T. caudatus) of which a 

 full description of even one sex could be obtained. 



It confirms KROYER'S genus diagnosis in all but two particulars. The second 

 maxillae are not forked at the tip like those of Lepeoplitheirus, but are simple and 

 pointed like those of Caligus. Furthermore the endopod of the fourth legs, instead 

 of being as large as the exopod, is reduced so much as to be rudimentary and contains 

 only two joints. These two particulars furnished data which will at once distinguish 

 the species from T. caudatus. 



SUB-FAMILY: EURYPHORIN^E. 



Dissonus,* n. gen. 

 



First thorax segment fused with the head to form the carapace, which is semilunar 

 in shape and about twice as wide as long. 



Second, third, and fourth thorax segments free, each' considerably wider than long, 

 the second one only provided with lateral plates. Genital segment not much 

 enlarged, without plates or processes, but with the entire ventral surface covered 

 with stout spines. In the male the fifth legs are seen on the posterior lateral 

 margins and the sixth pair at the posterior corners. Abdomen small, one-jointed in 

 both sexes ; anal laminae of medium size and armed with large plumose setae. 



Egg-strings four-fifths of the entire length and not quite as wide as the abdomen. 

 Eggs large, about forty in each string. 



Antennae and mouth-parts like those in the Caliginae. Second maxillae longer than 

 the mouth-tube and bifurcate at the tip. First maxillae and furca wanting. Mouth- 

 tube short and triangular in shape with a rounded tip, jointed transversely near the 

 centre. The four pairs of swimming legs biramose ; rami of the first pair two- 

 jointed, of the other pairs three-jointed ; spines and setae almost exactly like those 

 in Trebius. 



Dissonus spinifer,t n. sp. Plate III., figs. 34 to 47. 



e. Carapace transversely semilunar, twice as wide as long ; the ventral 

 surface around and outside of the second antennae is raised somewhat, and beneath it 



* Dissvntis, disagreeing or different, i.e, not agreeing with any of the established genera. 

 t Sjnnifer, bearing spines (on the ventral surface of the genital segment). 



