HOLOTHTJRIOIDEA OF THE INDIAN OCEAN. 179 



Sub-genus Actinopyga.* Bronn. 



AcTiNOPYGA SERRATiDENs. Pearson. 



(PI. XXIX., fig. 5.) 



Actinopyga serratidens, Pearson 1903 (18). 



This species was named and described by the present writer 

 in 1903 from a single specimen obtained by Professor Herdman 

 from Galle, Ceylon. Since then it has not been recorded. 

 Amongst the Holothurians collected by Mr. Crossland at 

 Suakim in the Red Sea, and sent to me by Prof. Stanley 

 Gardiner, are several specimens of this species. During a two 

 months' inspection cruise on the Ceylon pearl banks early 

 in 1913, 1 found this species extraordinarily abundant. With 

 the exception of Halodeima atra, which appears to be the 

 predominant Holothurian along the Ceylon coast, and Bohad- 

 schia marmorata and Thymiosicya scahra, which are abundant 

 though limited in their distribution, I consider the above 

 species the commonest form in the littoral waters of Ceylon. 

 It is also one of the largest Holothurians I have seen, and 

 frequently attains a size of 400 mm. 



External Appearance. — Without exception the Ceylon 

 specimens are uniformly black, with a faint suggestion of 

 dark brown. All the Red Sea specimens, except one, on the 

 other hand, are black above and yellowish-white below, and 

 at first sight resemble Actinopyga mauritiana. The single 

 exception is similar to the Ceylon specimens in colour. 

 Out of more than one hundred specimens from Ceylon waters, 

 all from the pearl banks, I have not seen one which has any 

 trace of Hght colour about it, with the exception of the pedicels, 

 which are sometimes white. The ambulacral appendages con- 

 sist of numerous pedicels evenly distributed over the trivium, 

 and small papillae scattered over the bivium and less abundant 

 than the pedicels. There are twenty dark brown tentacles. 



The anal teeth are large and yellow and irregular in shape, 

 producing the serrated appearance referred to in my original 



*For definition see Pearson, Spolki Zeylanica, Yol. IX., Part XXXV 

 p. 169. 



