132 SPOLIA ZEYLANICA. 
do not eat oysters. Examples include Rhynchobatus djeddensis, 
Myliobatis nieuhofi, Pteroplatea micrura, Pristis cuspidatus, and 
possibly Rhinoptera javanica, all of which most probably have their 
own particular article of food. 
(5) Encysted Tetrarhynchids in Teleosts. 
There are many Teleosts which feed on oysters. Amongst them 
may be mentioned— 
(1) All members of the genus T'etrodon. 
(2) Balistes mitts, Balistes undulatus, and Balistes stellatus. 
(3) Lutjanus argentimaculatus, and possibly other members of 
this genus. 
(4) Serranus undulosus, and possibly other members of this 
genus. 
The above list is not intended to be a complete one, but oysters 
have been found in the stomachs of all the species named. Tetra- 
rhynchid cysts only are in almost every case (and particularly in 
Balistes, Lutjanus, and Serranus) found in numbers in the intestines. 
Cysts have not been found in any species of the genus 7'etrodon. 
These combined facts led to the original idea that Balistes might be 
an intermediate host of the pearl-inducing worm, although later 
Shipley and Hornell pointed out the difference between the Tetra- 
rhynchids found encysted in the oyster and those encysted in the 
intestines of Balistes. Several species of Tetrarhynchids occur 
encysted in the intestines of the Teleosts previously named, and 
they are undoubtedly derived from the cysticercoids present in the 
different molluses eaten. 
Encysted forms of Tetrarhynchus unionifactor also occur, 
particularly in Balistes and Serranus. Recent work has shown that 
the encysted form of Vetrarhynchus uniontfactor which occurs in 
Serranus and Balisies is exactly similar to that encysted in the 
oyster. Shipley and Hornell appear to have been wrong in stating 
that ‘“‘ The more advanced larve from the pearl oyster have arrived 
at a later stage in development than the larve found in Balistes.’’* 
It is certain that my encysted Tetrarhynchus unionifactor from 
Balistes is not the same species as those described by these 
authors from Balistes. However, the fact remains that encysted 
Tetrarhynchids have been obtained from Balistes and Serranus 
which are exactly similar to the encysted Tetrarhynchid found in 
the oyster. The spines and general appearance are exactly similar, 
and the only difference noted was that those found encysted in 
Teleosts were very slightly larger than those obtained from the 
oyster. 

* «« Ceylon Reports,” Vol. II., p. 78. 
