88 CEYLON PEARL OYSTER REPORT. 



from Trygon centrura. Diesing* has also described T. {Kit.) rubromaculatus from 

 Trygon pastinaca, and T. {Hh.) heteromerus from Trygon brucco, but the Trygons 

 from the seas around Ceylon have yet to lie investigated for their Cestode parasites. 

 None of these Tetrarhynchi hitherto described from Trygons sufficiently resemble tbe 

 forms described in this Memoir to warrant any claim to relationship. 



Systematic Description. 



The following is an attempt to draw up the systematic characters of the three 

 Tetrarhynchids described above, but it must not be forgotten that these characters 

 are taken from larval forms. Although the later stages of the larva? obviously 

 approximate to the adult condition, the characterisation of a species from a larval 

 form is always open to objection. 



Cestodes from Pearl Oyster. 



1. Tetrarhynchus unionifactor, n. sp., Plate II., figs. 19 and 20. 



Well advanced larva, about 6"5 millims. to 7 millims. in length. Head with two 

 lappets at the bottom of each two bothria. Introverts with teeth spirally arranged, 

 teeth shaped as in figure, uniform in shape and size. Surface of body covered with 

 low warts except the hindermost end, where the last thirtieth of the total body 

 length was ornamented with coiling markings, perhaps post-mortem wrinkling. The 

 posterior half of this region hears stiff cilia, The sacs of the introverts stretch 

 throughout the anterior half of the bodv. There is no trace of vesicle. 



Habitat : In the tissues of the pearl oyster. Margaritifera vulgaris, Schum , from 

 the Gulf of Manaar, Ceylon. 



Cestodes from File or Trigger Fish. 



The three Cestodes hitherto recorded from the genus Batistes, and they are all 

 from Batistes capriscus, L., are : 



(i.) Rhynchobothrium paleaceum, Rue, which in a larval state is found in Mullus 

 barbatus, L., and is a synonym of Tetrabothriorhynchus migratorius, Dies.1' 

 According to von Linstow's ' Compendium der Helminthologie ' this species 

 is figured in Oisson's " Entozoa, iakttagna hos Scandinaviska hafsfiskar."| In 

 the explanation to the Plate, however, the Cestode is simply called a Tetra- 

 rhynchus without specific name. 



* ' S.-B. Ak. Wien,' XLVIII. 



t 'Diesing 'Systenia Helminthum,' p. 573, and 'Rev. d. Cephal. Param.,' 'S.-B. Ak. Wien,' XLVIII., 

 p. 294. 



\ 'Lund. Univ. Ais-skr.,' 1886 (IV.), Plate II., figs. 35, 36, 37. 



