176 CEYLON PEARL OYSTER REPORT. 



a very well-marked carina running down the whole of its median dorsal length 

 and terminating in the postero-dorsal spine. Last three thoracic segments exposed 

 behind the carapace ; all the abdominal segments with their postero-lateral angles 

 very acutely drawn out into spinous processes ; sixth abdominal segment with a pair 

 of median dorsal spines on its posterior border. 



Telson (fig. 23) quite flat, without carinae of any sort, but a series of well-marked 

 concentric pits present, about one and a fifth times longer than broad, six marginal 

 spines, well developed, acute, and slightly curved : margin between the submedian 

 spines deeply emarginate, with a slight notch in the centre, and bearing seventeen 

 denticles on each side ; eleven intermediate and a single lateral denticle present on 

 each side. 



Uropods (fig. 24) barely reaching the level of the lateral spines of the telson ; 

 traces of six spines on the external edge of the outer branch ; inner spine of the basal 

 prolongation slightly longer than the outer, but not yet reaching the tip of the outer 

 uropod. 



Eyes somewhat large, placed on slender stalks. 



Raptorial claw (fig. 25) with no signs of teeth as yet on the dactylus, two 

 prominent teeth at the proximal end of the propodus, the inner margin of which is 

 spinulose. 



Last three thoracic appendages present and biramous, but still very small. 



Abdominal appendages well developed, with gills just showing. 



The smallest larva belonging to this species in the collection measures 4"5 millims. 

 in length (fig. 20). It has the carapace rather wider, proportionally, than older 

 larvae, but the median dorsal carina is already very well marked. There are three 

 spines on the ventro-lateral edge of the carapace between the antero- and postero- 

 lateral spines, and a single secondary spine on the latter. The telson (fig. 21) is of 

 somewhat different shape to the older larvae, being much more quadrangular, with the 

 marginal spines much shorter. The margin between the submedian spines is relatively 

 much wider and more shallowly emarginate, without a trace of median notch. The 

 telson bears seven submedian, five intermediate, and a single lateral denticle on 

 each side. 



The next stage, 7 millims. long, has a carapace much as in the last. The telson, 

 however, has assumed a much more octagonal shape (fig. 22), and the margin between 

 the submedian spines is relatively much narrower and more deeply emarginate than 

 in the larva of 4 - 5 millims. The marginal spines are much more prominent, and there 

 are fourteen submedian, ten intermediate, and a single lateral denticle on each side. 



After 7 millims. the larva assumes practically the same shape as described above 

 for a 27 millims. larva, and a slight notch appears in the margin of the telson between 

 the submedian spines. The marginal spines likewise become longer and more acute. 



This Alima is most closely allied to Alima bidens, Glaus. The latter is the only 

 Alima, as far as I am aware, which has a well-marked median carina on the carapace, 



