THE CEYLON PEARL-OYSTER. 291 
Myzorhynchus uniformly muscular, without obvious division 
into muscular tracts; retractile within an annular collar; in 
section it may appear either conical, Jenticular, or flattened, 
concave and sucker-like ; protrudes as a conical papilla when in 
locomotion. ‘This anterior muscular region, including the collar, 
is about one-third of the total length of the larva when extended. 
The whole myzorhynchus can be protruded, the collar then 
forming an annulus around it. 
Collar or cephalic sheath muscular with denticulated cuticle, 
the denticles tricuspid. (Herdman’s Report, Part II. (Shipley & 
Hornell, Parasites of the Pearl-Oyster) pl. i. figs. 10,11, & 14, 
pl. i. fig. 18; also Pt. V. (Pearl- Production) pl. iii. fig. 9.) 
The denticles measure from 3 « to 5 u in diameter. 
Hinder part of the larva centrally parenchymatous, the 
parenchyma containing the calcareous corpuscles characteristic 
of Cestode larvee, peripherally more muscular. 
The hinder part of the body is covered by a thick, radially 
marked epicuticle, permeated by numerous closely-set tubuli, 
and suggesting on superficial examination a coat of cilia. This 
epicuticle varies in thickness but is generally about 0:03 mm. 
thick, and the true cuticle lies under it. 
This form is distinguished from the next described worm by its 
larger size (Her dman gives the size as about six times that of the 
smaller form), the undivided musculature of the myzorhynchus, 
and the wider and more open character of the collar-sheath of the 
myzorhynchus in the resting-stage. 
Habit. Resting in spherical tibrous cysts, derived from the 
connective tissue of the host, in the Ceylon Pearl-Oyster, 
Margaritifera vulgaris. Most frequent in the visceral mass, 
notably the liver. 
Habitat. Gulf of Manaar (Herdman & Hornell). Trincomalee 
( Willey). 
The following is a description of a worm which I regard as 
in all probability the adult of this larva. The single specimen 
was obtained from the spiral intestine of Aétobatis narinari, by 
Mr. Hornell, on 4th January 1905, and had apparently been 
overlooked by Mr. Shipley among some duplicate specimens of 
Kystocephalus translucens, along ‘with which I found it when 
examining Dr. Shipley’s material. After it had been cleared and 
examined as a transparent object, Dr. Shipley very kindly allowed 
me to have sections cut from it to compare with those of the 
larva in the pearl-oyster. 
(2) Adult of Lylocephalum ludificans, Spa pe , (Pls: Xb Vaes& 
XLVII. figs. 60-64.) Length 12mm. Head 0°6 mm. long by 
0-5 mm. broad ; pyriform, slightly broader in front than behind ; 
transition from head to neck not very sharply defined. The 
myzorhynchus in this specimen is retracted within its sheath, as 
is usually the case with the larva in the pearl-oyster; it is about 
*3 mm, in diameter. Around the head are four marginal suckers 
about *125 mm. in diameter. Proglottides about 140 i in number, 
increasing but little in breadth from before backwards ; they 
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