1918.] 



N. Annandale : Molluscs of tlie Inle Lake. 



1^5 



posed of convex, concentric layers of shell-substance. The layers are 

 often oblique, but not so oblique that the layer is directed outwards 

 or forwards on the shell. In similar sections of the shell of Margarya 

 and Taia the layers of shell-substance are nearly straight, and project 

 outwards and forwards in the form of well-defined lamellae. In a 

 longitudinal section the appearance of the layers would be hardly 

 different in Tulotoma, but in the other two shells they would be con- 

 vex and more or less concentric. This is evident from the fact that 

 the prominences in the American shell are arched both longitudinally 

 and transversely, whereas in the Asiatic shells their convexity is longi- 

 tudinal ; horizontally they project almost flat. 



Key to the Shan Species of Taia. 



A. Shell somewhat globosely conoidal. 



1. Shell almost subumbilicate, with the spiral ridges 



always present but never strongly developed and 

 never regularly tubercular or squamous 



2. Shell entirely non-umbilicate, with some or all of 



the ridges distinctly tubercular if at aU well 

 defined, sometimes almost absent. 

 («) Shell obese, thick, with the microscopic sculp- 

 ture on the apical whorls resembLmg a web 

 of fine cloth, with the spiral sculpture gra- 

 nular or tubercular 

 (h) The microscopic sculpture of the apical whorls 

 less well developed ; sheU as a rule longer 

 and less obese, 

 (i) Spiral sculpture extremely variable ; a 

 regular series of subspiniform scales 

 never present on body-whorl 

 (ii) Spii-al sculpture much more constant, 

 granular or tubercular, sometimes with 

 a regular series of subspiniform scales 

 on the body-whorl 



B. SheU elongate-conoidal. 



1. Elongation of shell moderate ; shell thin ; a regular 



series of subspiniform scales present on the body- 

 whorl 



2. Elongation of shell considerable, suture extremely 



oblique above body-whorl ; scale-like projections 



on body-whorl, if developed, never spiniform. 



(i) Shell large (length 45-60 mm.), extremely 

 elongate 



(ii) SheU smaUer (length 35-37 mm.), less elon- 

 gate 



C. SheU conical. 



1. A regular series of subspiniform or spiniform scales 



never produced on the shell 



2. A more or less regular series of spiniform or sub- 



spiniform scales present on the body-whorl. 



(i) Scales on body-whorl spiniform, regular ; 

 shell not exceeding 32 mm. in length, nar- 

 rowly conical, constant 



(ii) Scales on body-whorl subspiniform, less re- 

 gular ; shell at least 35 mm. in length, 

 less narrowly conical, variable in size, 

 shape and sculpture. 



(a) Scales on body-whorl irregular ; shell 

 at least 45 mm. in length, thick ... 



{b) Scales on body-whorl more prominent 

 and less irregular ; shell as a rule 

 less than 40 mm. long, thinner 



T. theobuldi. 



T. ohesu. 



T. naticoides. 

 T. intermedia. 



T. shanensis. 



T. cylindrica. 

 T. lacuatris. 



T. unaloga, 

 T. intha. 



T. conica. 

 T. elitoralia. 



