124 ‘ CONTRIBUTIONS 
the edge; whorls four, perfectly square; mouth quadraii- 
cular. i 
Length 1-20th, Breadth 3-20ths, of an inch. 
The smaller figure is of the size of nature. 
Observations. This curious and interesting little species 
is the only perfectly flat shell Lam acquainted with. The 
Pleurotomarium tuberculosum of Defrance, as figured by 
Blainville, has in its general form some resemblance to it. 
Its sinus, its rounded mouth and somewhat convex spire, 
render it impossible to confound even the genera. 
GENUS PLANARIA.* Brown. (Maclurite? Lesueur.) 
P. nitens. Plate 4. Fig. 113. 
Description. Shell discoidal, impressed above and below, 
smooth and shining, diaphanous; substance of the shell 
very thin and fragile; whorls three, convex; mouth lunate; 
outer lip reflected. o>} hal 
Length less than 1-20th, » Breadth less than 1-20th, of an inch. 
The smaller figure is of the size of nature. 
Observations. 'This very minute species is so fragile that 
I have found it impossible to secure a perfect specimen. It 
resembles closely the P. alba (Brown), but that shell has 
not a reflected margin. I have found a single specimen 
only with this part perfect enough to show this char&ete 
a ll 
* Established by Capt. Thomas Brown of Edinburgh for some small 
species found on the coast of Scotland. - 
