180 CEYLON PEARL OYSTER REPORT. 



Lysioerichthus a. Plate II., tigs. 30 to 34. 



Localities : 



Off Kalpentyn Island, surface tow-net, all night. One, 8 millims. 



Cheval Paar, surface tow-net. One, 8 millims. 



Off Mutwal Island, surface tow-net. One. 7 millims. 



This species is very closely allied to L. ophthalmicus, Hansen, from which it chiefly 

 differs in having a pair of spines on the postero-median border of the sixth abdominal 

 segment. 



Carapace (fig. 30) rather small and compact ; rostrum short, about one-half of the 

 total length of the carapace, no ventral teeth ; antero-lateral spines very small 

 indeed ; postero-lateral spines rather short, not reaching to the posterior end of the 

 first abdominal segment, without secondary spinules ; postero-median dorsal spine 

 and lateral spinules of any kind absent. 



Abdomen with all the segments developed, and having their postero-lateral 

 corners acutely angulated ; pleopods all well developed, but no rudiments of gills 

 present ; sixth abdominal segment with a pair of median dorsal spines on its posterior 

 border. 



Telson about as long as broad, six marginal spines present ; margin between the 

 submedian spines almost straight, without trace of median cleft, and bearing twenty- 

 four submedian denticles ; one intermediate denticle present between the submedian 

 and intermediate spines of each side ; no lateral denticles. 



Uropods (fig. 3 1 ) fairly well developed, extending as far as the level of the lateral 

 spines of the telson ; traces of four spines on the external margin of the outer branch ; 

 outer spine of the basal prolongation very much longer than the inner one. 



Second to fourth thoracic appendages (figs. 32 to 34) agree in essential details with 

 those figured by Hansen for L. ophthahuicus. 



Last three thoracic appendages, though still very imperfectly developed, are, 

 however, already biramous. 



Length 8 millims. 



The specimen, 7 millims. long, agrees well with the above description, but is 

 generally less developed, having only three spines on the outer uropods, and the last 

 three thoracic appendages are mere buds. It has also only twenty-two submedian 

 denticles on the telson. 



Among all described Lysioerichthii the present species comes nearest to L. ophthal- 

 micus, Hansen (1895), from which it differs (1) in having a pair of submedian spines 

 on the posterior border of the sixth abdominal segment, and (2) in the relatively 

 smaller size of the inner spine of the basal prolongation of the uropods. 



Lysioerichthus /3. Plate III., figs. 35 to 40. 

 Localities : Muttuvaratu Paar, surface tow-net. Two hundred and seventy-five 

 specimens, from 2 millims. to 6 millims. in length. 



