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



tions on the living Taia that would have thrown any light on this 

 point, but I have been able to examine some well-preserved speci- 

 mens of T. intha in which the animal is partially expanded and 

 the mantle not completely retracted. In those in which the 

 growth-period was completed when they were killed I can tind no 

 peculiarity in the margin of the mantle, which is either quite 

 smooth or undulates gently, but in several specimens in which the 

 extreme thinness of the lip proves that growth was still in progress, 

 the base of the youngest scale-like projection of the peripheral 

 ridge is still hollow and contains a broad lobe of the mantle-edge, 

 evidentl}' temporarj' in nature. 



The projections on the ^hell, however, are not only of consider- 

 able length when highly developed, but contain a relatively large 

 amount of calcareous matter. In both Taia and Margaryu the 

 calciferous glands degenerate greatly in the periods of rest and in 

 full-grown individuals become very uniform all along the edge of the 

 mantle, but in a young growing specimen of the Taia intha I find that 

 immediately opposite the peripheral ridge there is a cushion-like 

 thickening of the supramarginal ridge due to the greater depth of the 

 glands at this point. In the individual in which this observation 

 was made a scale-like projection was in the process of formation. 

 In others, in which this was not so, the glands at the same point 

 were not hypertrophied to an^' appreciable degree. 



It follows, therefore, that the projections are formed owing 

 to periodical hypertrophy of the calciferous glands in the part of 

 the mantle that lies immediatelj' beneath the ridge on the shell, and 

 moulded into shape by temporary lobes of the mantle edge. The 

 difference between the smooth ridges on the shell of such species as 

 Vivipara lapilloruin and the interrupted ridges, often with relatively 

 long projections, of such forms as Taia intha or the var. carinata 

 of Margarya melanoides is probably^ therefore, due to the local 

 hj'pertroph}' of the calciferous glands being in one type of shell 

 permanent, and in the other temporary. Elongate projections 

 on the ridges of the most highly sculptured shells of the family 

 are secreted thus and are modelled into shape b^^ the temporary 

 lobes. It is noteworthy that whereas the muscles are not so 

 coarse, and the transverse fibres distinctly less well- developed, 

 in the marginal region of the mantles of Taia and Margarya 

 than in the smooth-shelled Lccythoconcha lecythis, the two former 

 genera have a regular network of muscles pervading almost the 

 whole mantle in a manner not observable in L. lecythis or am' 

 other species of the family^ examined. This may doubtless assist 

 in the projection of temporary lobes from the edge of the mantle. 



The secretion of the periostracal glands probably mixes to 

 some extent with that of the calciferous glands and forms the 

 organic basis of the shell. 



The dark margin of the mouth of the shell to be noticed in 

 many species of Vivipara when the growth-period is complete is 

 probably due to a general suffusion of black pigment correlated 

 with its accumulation in the tissues at such periods. 



