98 CEYLON PEARL OYSTER REPORT. 



then posteriorly. Thus the animal moves one step forwards and is brought back to 

 the attitude it had at the bep-inninsr. 



In Bronn's Trematoda, Braun enumerates four species of Aspidogaster, viz., 

 A. conchicola, v. Baer, A. limacoides, Diesing, A. insignis, Lediz, and A. mac- 

 donaldi, Mont. In his recent revision of the family Aspidobothridre, Nickerson* 

 places the third of these, A. insignis, in the genus Cotylaspis, thus reducing the 

 number of species of Aspidogaster to three. Of these three our species is most 

 clearly allied to A. macdonaldi, inasmuch as these two species, and these two species 

 alone, ai'e provided with the remarkable "tentacles" or "tube-feet" which project 

 between the suckers of the foot. It however differs from this species in the following 

 particulars : (i.) Macdonald's specimens were tallowy in colour, while ours are of an 

 ochreous brown with a deep, rose-pink foot ; (ii.) Macdonald's specimens were - inch 

 to xo mcn m length, ours are inch long ; (iii.) Macdonald mentions " caeca" in the 

 intestine of A. macdonaldi, ours have a simple alimentary canal, possibly Macdonald 

 has made a mistake in this respect ; (iv.) Macdonald records some 180 tentacles 

 and some 120 alveoli or suckers, the numbers in our specimens are fewer ; (v.) Mac- 

 donald found his specimens " creeping about in the respiratory siphon of a large 

 Melo, or melon-shell, in Shark Bay, Western Australia," our specimens occurred in 

 the pericardial chamber of Margaritifera vulgaris, Schum., on the Cheval Paar, 

 Ceylon. 



At the end of his paper Nickerson raises the question as to whether Macdonald's 

 species does not deserve generic rank. If it does it carries our species with it. 

 The chief generic character would be the possession of the tentacles or " tube-feet." 

 At present, and until more specimens have been investigated and until we know 

 more of the life-history, it seems wise to regard these forms as well-marked species 

 of Aspndogaster. 



III. NEMATODES OF THE PEARL OYSTER, AND OF THE 



FILE FISH. 



The only previous record of a Nematode from the pearl oyster that we have been 

 able to find is in a list by Dr. L. Obley of the Nematodes in the British Museum, t 

 where the name appears of Ascaris melcagrina, Kollar, from the pearl oyster. 

 Vincenz Kollar wrote almost exclusively on insects, and we were unable to trace 

 any reference to this Nematode in such of his writings as we have been able to 

 inspect. We therefore applied to Mr. C. D. Sherborn for help. Together with 

 Professor F. Jeffrey Bell, he very kindly made an inspection of Orley's MS., 



* ' Zool. Jahrb. Syst.,' XV., 1901 to 1902, p. 597, Nickerson makes no mention of A. valid, Stors, 

 described in a Memoir I have not seen, from the (esophagus and stomach of Thalassochelys caretta 

 (M. Stossich, 'Appunti di Elmintologia '). 



t ' Ann. Nat. Hist,,' IX., oth Series, 1*82, p. 310. 



