130 CEYLON PEARL OYSTER REPORT. 



the level of the antrum femininum is almost reached. The structure of this part is 

 similar to that of its first part. Finally it ends by opening in the middle line into a 

 large crescentic accessory vesicle (accves.), whose "horns," lying one on either side of 

 the middle line, are directed forward. The two halves of the accessory vesicle end in 

 large, rather rounded lobes (I.). Its walls are composed of an active secretory 

 epithelium which is at first columnar, but becomes more cubical in the lobes. These 

 lobes contain a quantity of thick spongy secretion. In this secretion mass lie a large 

 number of remarkable spindle-shaped bodies which vary considerably in size, and 

 stain very deeply. They are shown in fig. 1, on the Plate. Each of these bodies lies 

 in a small clear cavity which is spherical in shape. In the sections it is, of course, 

 seen as a clear round patch, in which the dark-stained spindle-shaped body lies 

 equatorially. The nature of these bodies is quite unknown to me, and the state of 

 preservation of the tissues in the single specimen prevents a more detailed description. 

 I am inclined to conjecture, however, that they may be spermatophores. In one or 

 two cases the clear space surrounding them seems to be occupied by a gelatinous 

 lightly-staining substance (x, in fig. 1 , on Plate). 



The most striking features of the genital apparatus of this species are (i) the great 

 length of the vagina and (ii) the shape of the accessory vesicle, which is, roughly 

 speaking, bilaterally symmetrical, The first of these peculiarities is paralleled in 

 Idioplana australiensis, a species described by Woodworth.* This species also 

 resembles that under discussion in the following respects : Distribution of the eye- 

 spots, coloration, and structure of the terminal parts of the male ducts. Conse- 

 quently we may conclude that the two are closely related. 



Idioplana, however, differs from Woodworihia in shape, in possessing a peculiar 

 notch on the anterior margin, and in the fact that the prostatic duct and the 

 vesicular duct open to the exterior almost independently of one another. 



Woodworihia, on the other hand, possesses an accessory vesicle which is bilaterally 

 symmetrical. These differences are sufficient to warrant a generic separation of the 

 two forms. 



Stylochus ceylanicus, n. sp. 



Three specimens from Cheval Paar. 



Measurement (of largest specimen). Length, about 47 millims. ; breadth, 

 27 millims. Genital aperture 4 millims. from hinder end of body. Tentacles 

 4 millims. apart. Buccal opening sub-central. 



Coloration. Judging from the preserved specimens, this must be, on the dorsal 

 surface, a dull yellow covered with very numerous small ill- defined black spots which 

 are absent in the area lying just over the brain. Ventral surface plain yellowish- 

 white. 



Eye-spots. Numerous spots lie close together about the base of either tentacle ; 



* Woodworth, 'Bull. Mus. Harvard,' vol. XXXII., No. 4, p. G3, Plate XXXII., figs 2-5, 1898. 



