18 Gr- O. Sars. 



convinced myself, that they represent the very same species 

 in different ages. 



The Estheria compressa of Baird, from India, looks, in the 

 form of the shell, so very like adult specimens of the present 

 form, that I am mnch inclined to regard it as the same species. 

 In any case it is not an Estheria; neither can the form he 

 records as Estheria Birehii from South Australia be- referred 

 to that genus, but is most probably a member of the genus 

 here treated of, or at least very nearly related to it. 



Description of tlie female. 



(PI. 2). 



The shell of fully grown specimens measures in length 

 about 10 mm., in height 7 mm., and this species accordingly 

 attains about the size of the European form Limnadia lenti- 

 cularis (Lin.). As, however, it becomes sexually mature long 

 before having attained to its full size, apparently adult and 

 ovigerous specimens may also be found of far inferior size. 



In fully grown specimens the shell, when seen from the side 

 (fig. 1), appears rather wide and of a somewhat triangular form, 

 with the umbones strongly prominent and occurring far in 

 front. The dorsal margin is nearly straight, and slopes rather 

 obliquely from the umbones to the posterior extremity. The 

 ventral margin is strongly curved in the middle, and joins the 

 anterior edge by a perfectly even curve. The anterior extremity 

 is very short and narrowly rounded at the tip, whereas the 

 posterior one is rather produced and obtusely truncated at the 

 tip, with the upper corner more distinctly angular than the 

 lower. 



Seen from above (fig. 2), the shell appears much compressed, 

 the greatest width scarcely exceeding 1/3 of the length, and 

 occurring in the anterior part, across the umbones. Both 

 extremities appear pointed, the posterior one more so than 

 the anterior. 



