292 DR. H. LYSTER JAMESON ON 
begin to increase notably in length from about the 85th back- 
wards. The largest hindmost segments are about *5 mm. long, 
and slightly longer than broad (fig. 64). The armature of the 
collar @ (in ‘figs, 61-63) is similar to that of the larva. In section 
(fig. 62) the myzorhynchus is seen to be retracted im such a way 
that its anterior surface is thrown into folds, thus resembling the 
condition of the larva shown in fig. 59. The only point in which 
the head of this worm appears to differ from the larva in the 
pearl-oyster is in the presence of the four marginal suckers, which 
may well be a feature first acquired in the final host. 
Tylocephalum minus, sp. n. (Plate XXXIIT. fig. 2.) (The 
smaller globular larva, which Prof. eran thinks may 
also be concerned in pearl-formation.) 
(Tetrarhynchus sp., Herdman.) 
For other figures see Herdman’s Report (Pearl Production), 
Part V. pl. ii. figs. 1-3, 17.4, 18-22; also text-figure 3, p. 19. 
Diameter of resting parasite in cyst from 0:07 to 0°2 mm. 
Average diameter of 40 examples shown on Prof. Herdman’s 
slides and measured by the present writer, 0°14 mm. Body sub- 
globular, consisting, as in 7’. ludificans, of an anterior muscular 
and a posterior parenchymatous part, the anterior muscular 
portion (myzorhynchus) consisting of a conical papilla in a ecup- 
flask-shaped depression formed by the surrounding muscular 
collar or sheath. As a rule, in preserved specimens, the opening 
of this depression seems relatively narrower, and the papilla more 
conical and less flattened than in the previous species. The 
musculature of the myzorhynchus shows, in some examples 
a tendency to break up into four longitudinal tracts. In 
young examples the myzorhynchus may be barely differentiated 
Cuticular spines are present on the collar, but they are smaller 
and relatively finer than in 7”. ludificans. The epicuticle is about 
°O1 mm. thick. 
This form is distinguished from 7’. ludificans by its smaller 
size and finer armature of the collar, and by the tendency of the 
myzorhynchus musculature to break up into four strands. It is 
regarded by Southwell as the same species as 7’. ludificans. 
Habit. Resting in spherical fibrous cysts in the connective 
tissues of Margar nitifer a vulgaris, occurring in the visceral mass, 
mantle, gills, ete. 
Habitat. Gulf of Manaar. 
Prof. Herdman, while he regards the form here named 
T. ludificans as the pearl-producer par excellence, considers that 
the present species too ‘*may occasionally form the nuclei of 
pearls” (Report V. p. 22). 
Particulars of the structure of both these forms are given on 
pp. 79-82 of Part IT. of Prof. Herdman’s Report. 
[34] 
