106 CEYLON PEARL OYSTER REPORT. 



that Plesiochorus is to be regarded not as a member of the Anaporrhutinae 

 themselves, but as the representative of a separate sub-family of the Gorgoderidas 

 allied to the Anaporrhutinae. 



Distomum, sp. (larva). Plate II., fig. 18. 



From Pinna, sp. One specimen. 



A small larva of a Distomid, about 1 inillim. long, and about 0'36 millim. broad, 

 without spines. Ventral sucker very large, projecting, situated in the posterior half 

 of the body, its distance from the posterior end of the body 0'20 millim., its diameter 

 0'33 millim. Diameter of the oral sucker 0*18 millim., of the pharynx 0'12 millim. 

 (Esophagus wanting. Intestinal coaca ending at about the middle of the body. 

 Excretory vesicle V-shaped, ending at about the same level as the posterior end 

 of the intestinal cceca. 



From the genus Gymnophallus, larval forms of which are found in some marine 

 Lamellibranchs (Mytilus edulis, Saxicava rugosa), this parasite of Pinna differs in the 

 absence of spines in the skin, of a distinct oesophagus, of an unpaired median trunk of 

 the excretory vesicle, and by the smaller length of the excretory vesicle. 



