292 DR. U. LYSTER JAMESON OX 



begin to increase notably in lengtli fi'om abont the 85th back- 

 wards. Th.e largest hindmost segments are about -5 mm. long, 

 and slightly longer than broad (lig. 64). The armature of the 

 collar a (in figs. (31-63) is similar to that of the larva. In section 

 (fig. 62) the myzorhynchus is seen to be retracted in such a Avay 

 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 diflfer 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 XXXIII. fig. 2.) (The 

 smaller globular larva, which Prof. Herdman thinks may 

 also be concerned in pearl-formation.) 



{Teirarhyndius sp., Herdman.) 



For other figures see Herdman's Report (Pearl Production), 

 Party, pi. ii. figs. 1-3, 17a, 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 T. ludificans, of an anterior muscular 

 and a posterior parenchymatous part, the anterior muscular 

 portion (myzorhynchus) consisting of a conical papilla in a cup- 

 or 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. 

 Caticular spines are present on the collar, but they are smaller 

 find relatively finer than in T. ludificans. The epicuticle is about 

 •01 mm. thick. 



This form is distinguished from 2\ 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 T. ludificans. 



^Ilabit. Resting in spherical fibrous cysts in the connective 

 tissues of Margaritifera vulgaris, occurring in the visceral mass, 

 mantle, gills, etc. 



Habitat. Gulf of Manaar. 



Prof. Herdman, while he regards the form here named 

 T. ludificav,s as the pearl-producer par excellence., considers that 

 the present species too "may occasionally form the nuclei of 

 pearls " (Report Y. p. 22). 



Particulars of the structure of both these forms are given on 

 pp. 79-82 of Part II. of Prof. Herdman's Report. 



