184 CEYLON PEARL OYSTER REPORT. 



This larva is distinguished among Gonerichthii hy the somewhat unusual character 

 of having the inner spine of the basal prolongation of the uropod much longer than 

 the outer. In no Gonerichihus yet described is such a character found. In other 

 respects the larva is a perfectly typical Gonerichthus, especially in the characters of 

 the third and fourth thoracic limbs, which have not the swollen propodus charac- 

 teristic of Lysioerichthii. The larva is very far advanced in development, but the 

 raptorial claw shows no signs of spines on the dactylus. It must be concluded there- 

 fore that the larva belongs to the genus Gouodactylus. 



Gonerichthus /3. Plate III, figs. 43 to 45. 



Locality : Off Kalpentyn Island, surface tow-net, all night. Forty-two specimens, 

 from 4 to 7 millims. in length from eye to telson. 



Carapace (figs. 44 and 45) with rostrum very long, the length from the antero- 

 lateral spines to the tip of the rostrum exceeding the length from the antero-laterals 

 to the posterior median dorsal spine ; eight small teeth on the ventral edge of the 

 rostrum ; antero-lateral spines very small ; postero-lateral spines very long, extending 

 to the junction of the sixth abdominal segment with the telson, a small spine at its 

 base projecting ventrally ; postero-median dorsal spine very short. 



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

 angles slightly angulated ; sixth segment with a pair of median dorsal spines on its 

 posterior border ; abdominal appendages very well developed, with digitate gills 

 already present. 



Telson rather longer than broad ; six marginal spines present ; margin between the 

 submedian spines emarginate, with a slight notch in the centre, and bearing twenty- 

 four submedian denticles ; two intermediate denticles present on each side, but no 

 lateral denticle could be discerned. 



Uropods well developed, extending to the level of the intermediate spines of the 

 telson ; traces of ten spines on the external margin of the outer branch ; outer spine 

 of the basal prolongation extending nearly to the level of the submedian spines of the 

 telson, much longer than the inner spine. 



Raptorial claw without traces of spines on the dactylus ; third and fourth thoracic 

 appendages of the usual Gonerichthus type, and not exhibiting the swollen propodus 

 of the Lysioerichthus ; last three thoracic appendages fairly well advanced and 

 already biramous. 



Length 7 millims. from the eye to the tip of the telson. 



The smaller larvas referable to this type differ chiefly in the proportional length of 

 the rostrum and postero-lateral spines, both of which increase in comparative length 

 as the larva advances (see fig. 43). 



This type evidently belongs to quite a small species of adult. At 7 millims. length 

 it is as far advanced as type ". at 11 millims., and is evidently not far from maturity. 

 It is one of the most abundant Erichthus larva? in the collection. 



