118 



Dr. F. R. Cowper Reed- 



degrees. Body of shell very gently convex, sharply marked ofE from 

 anterior ear ; umbo acute, directed forwards, situated at about 

 one-third length of hinge-line or subterminal. Surface of shell 

 covered with strong regular, concentric undulations, triangular 

 in section, of equal or subequal strength and size, becoming less 

 regular on anterior ear and smaller and weaker on posterior portion 

 of shell, with fine, straight, radiating lines crossing them in middle 

 part of valves. Some fine concentric lines are also occasionally 

 present on the undulations. Dimensions : (I) height (oblique), 

 30 mm. ; length (parallel to hinge-line), 23 mm. (II) height 

 (oblique), 80 mm. ; length (parallel to hinge-line), 55 mm. 



Fig. 1. — Posidonomya Becheri Bronn, var. nov. siamensis. 



Remarks. — This is the species which occurs on the small broken 

 image of a Buddha from the temple of Bah Nah. There are several 

 more or less perfect examples of various sizes on it, and one shows both 

 valves in juxtaposition and well preserved. The largest specimen is 

 imperfect. The ornamentation is like that of Posidonomya Becheri 

 Bronn ; ^ but with regard to the characters of this genus there is 

 considerable diversity of opinion. Zittel says it has no ears, whereas 



' Wheelton Hind, op. cit., vol. ii, p. 27, pi. vi, figs. 11-15. 



