192 1 J N. Annandale & R. B. S. Sewell : Viviparn. 247 



of Vivipara, the third or lowest priraar}' ridge remains conspicuous 

 as a peripheral carina, even when the other two disappear or become 

 obsolescent. 



Ornamentation of the adult shell. 



In the adult shell, as I have already pointed out, the peri- 

 ostracal sculpture is relatively unimportant. In manj- species of 

 the family, including the great majority of those of Vivipara, 

 t)ie test-sculpture is not much more conspicuous. In V . benga- 

 Icnsis the oblique longitudinal lines on the periostracum are 

 impressed on the test and remain distinct through life. Indeed, 

 they are coarser and more prominent in the younger whorls. In 

 most races and phases of this species the spiral sculpture disap- 

 pears almost completely on the body-whorl, but in some indivi- 

 duals of certain phases and races, such as the phase halophita, 

 Kobelt (pi. II, figs. 9, 10), and the race balteata, Benson, the pri- 

 mary spiral ridges and also a few of those of the secondarj' order 

 are slightly thickened on the body-whorl, while in the Biumese 

 race (doliaris, Gould, pi. I, fig. 9) both the uppermost of the three 

 primarj' ridges and the peripheral ridge are prominent, forming 

 more or less sharp-cut angles in the outline of this whorl. In V . 

 oxytropis and a few other species of the same genus the peripheral 

 ridge forms a prominent keel on the body-whorl, separating the 

 shell into an u^jper and a lower region, while some or all of the 

 other ridges remain more or less salient. 



It is, however, in such forms as the more highly developed 

 species and varieties of the genera Taia and Margarya that the 

 sculpture of the test reaches its highest development in the adult 

 shell. In V. oxytropis ' the ridges are smooth and sharp : in the 

 more highly developed forms of the two genera mentioned they 

 are broad and coarse and are broken up into numerous tubercles, 

 scales or spines. Even in shells witli a comparatively simple 

 sculpture such as those of Taia tJieobaldi ^ or Margarya mclanoides 

 var. mansiiyi ^ the ridges have not the unbroken surface of those 

 on the shell of V. oxytropis and other ridged forms of Vivipara. 



In all the Viviparidae in which I have examined both em- 

 bryonic and adult shells, the ridges of the test are grooved inter- 

 nally at first. They retain this structure in V . oxytropis through- 

 out life. In some other ridged species and races of Vivipara, 

 however, with thicker shells, and also in all forms of Taia and 

 Margarya, the internal groove becomes more or less completely 

 obliterated by the deposit of nacreous matter on the internal 

 surface. 



In describing the ornamentation of the embrj^onic shell I have 

 alluded briefly' to the fact that in Taia iiitha and some other Vivi- 



Hanley and Theobald. Conch, hid., pi. l.xxvi, fig. 5 (1S76). 

 Annandale, Rec. Ind. Miis. .\.IV, pi. xvi, fig. i (19181. 



Kobelt on Viviparn. in Mart, and Chenin.. Couch. Cab., new edit , J^Tv*' 

 xxxvii, figs. 6, 7 (1909). ^O/^^* 



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