106 CEYLON PEARL OYSTER REPORT. 



that Plesiochorvs is to be regarded not as a member of the Anaporrhutinse 

 themselves, hut as the representative of a separate sub-family of the Gorgoderidse 

 allied to the Anaporrhutinae. 



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



From Pinna, sp. One specimen. 



A small larva of a Distomid, about 1 millim. 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 - 20 millim., its diameter 

 0"33 millim. Diameter of the oral sucker - 18 millim., of the pharynx 0"12 millim. 

 (Esophagus wanting. Intestinal coeca 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 coeca. 



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. 



