254 Records of the Indian Museum. [Vol. XXII, 



faces of the mantle a thin layer of undifferentiated connective 

 tissue can also be distinguished. It is thicker at some places than 

 at others but has no particular feature of interest. 



Musct.es. — The muscular system of the mantle is complex in 

 all genera of the family, but more so in some than in others. In 

 Vivipara it is comparatively simple. In this genus a relativelj' thin 

 sheet of longitudinal fibres extends down the external surface as 

 far as or nearly as far as the upper hmits of the supramarginal 

 ridge. This may be called the externai. retractor of the 

 MANTLE. In a corresponding position on the internal surface a few 

 fibres of a similar nature can be distinguished, but they are poorly 

 developed. In the neighbourhood of the supramarginal ridge a 

 strand of oblique or nearly transverse fibres runs along parallel to 







/ 



Fig. lO. — Microphotograph of vertical section tliri>ngh the edge of tfie mantle 

 in Margarya melanoides var. cnriiiatn, Nenniavr. The ciliated epithelium has 

 been removed from the surface below the shell -glands. 



6.S., blood-sinus; e., epithelium ; m., external retractor muscle; m'"., muscular 

 network; s.j., calciferous gland; y.j., yellow granules. 



the margin rather deeper in the tissues and forms the sphincter 

 OF THE mantle. Its structure is simple in this genus and it is 

 not powerfull}- developed. Finally, the external retractor sends 

 numerous fine branches obliquely into the thickness of the mantle, 

 in which they ramify and anastomose to form a loose muscular 



NETVi^ORK. 



In other genera the same elements of musculature are found, 

 but variouslj' developed. In Taia and Margarya, in which the 

 sphincter is still more feebly developed, the muscular network is 

 closer and has much smaller meshes and the individual strands are 

 finer. In Margarya, in which the mantle is greatly thickened, it 

 is better developed than in Taia. 



