•210 CEYLON MARINE lilOLOGIf'AL REPORTS. 



The larvso tlxomselves were large and flesliy, each measuring 7 mm. long and 3-5 mm. across the 

 proboscides. Strobila absent. 



Shipley and Horncll (Part V., " Ceylon Pearl Oyster Reports," page 70) describe cysts obtained 

 from Sphyrcena commcrsoni as follows : — - 



" The cysts are large forms ^•arying in length between 8 mm. and 30 mm., with a breadth of about 

 3 mm. They belong to Vaullegeard's Tetrarhynchus erinaceiis series, being enclosed in a vescicle as well 

 as in a cyst, which latter is apparently formed by the tissues of tlie host. The teeth were very crowded 

 and the excretory opening was ^^siblc, but little else could bo made out." 



Most probably these larval forms are similar to ours. 



The adult Tetrarhytichus gangeticus, Shipley and Hornell, was obtained from Carcharias gangeticus, 

 Miill. and Henle. 



So far as I have been able to make out, these specimens fall naturally into the genus Rhynchoboth- 

 rium, Rudolphi, which genus, according to Linton, is characterized as under : — 



" Body tseniaeform. Jfeck tubular. Head continuous witli the neck, with two opposite bothria, 

 parallel or converging at the apices, lateral or marginal, entire or midivided, or either bilocular with a 

 longitudinal partition or bilobed or divided. Proboscides four, terminal, filiform, armed, retractile in the 

 neck, for the most part longer than the head. Genital apertures, male marginal, female lateral, or male 

 and female marginal aiij)roximate." 



Otohothrium insigne, Linton (14 and 15). (Plato II., Figs. 19, 20, and 21.) 



Except the species described in this Report , no adult forms of the genus Otoboihrium have ever been 

 recorded from the pearl banks, but the encysted larvaj of this species are the most common larvae 

 obtained from certain marine fishes in the gulf. 



They occur in immense numbers encysted in the pharynx and in the mesenteries of all the species 

 of Balistcs and Serranus recorded from here. Tliey are also comnion in Diagramma, spp., and Stomateus 

 niger. The cysts measure on an average 30 mm. by 7 mm., but many forms are less. The cysts are 

 roughly club-shaped, the narrow end being clear and transparent, whilst the broader end is gray black, 

 due to the presence of a somewhat brittle layer of black pigment. Other cysts are perfectly transparent. 

 • Possibly these are younger forms. 



Both these kinds of cysts occur together, and along with them there often occur numbers of what 

 appear to be degenerate cysts. These are usually flattened, black, and have a powdery, Umey consistency. 

 No trace of a larva is to be foimd in them. 



The larvae in the healthy cysts measure 4 mm. in length. The breadth across the bothridia and the 

 posterior end is 1-5 mm. The breadth is rather less behind the bothridia. No strobila are present. 

 The larva can easOy be seen as a milky -white object within the cyst. The specimens answer perfectly to 

 Linton's description of Otohothrium insigne and to his figures. The bothridia are lateral and diverging, 

 and there are four accessory bothridial organs. The hooks are of various shapes. Linton gives the 

 length of the adult head and neck as 4 -2 mm. Our larval forms measure 3 nam. The adult form was 

 obtained from Carcharhinus obscurus. 



The habitat of our larval forms was as follows : — 



(1) Diagramma crassispinum. Twenty-five specimens. February 10, 1911. 



(2) Batistes, sp'p. Twelve specimens. Januaiy 20, 1911. 



(3) Stomateus niger. Eight specimens. February 10, 1911. 



(•i) Serranus undulosus. Over two hundred specimens. February 10, 1911. 



Otohothrium linstowi, n. sp. (Plate II., Figs. 22, 23, and 24.) 



The head consists of two imdivided saucer-like bothridia, the edges of whicli are usually reflected 

 back round the bothridium into an overhanging ledge. At the posterior margin of each bothridium are 



