124 CONTRIBUTIONS 



the edge ; whorls four, perfectly square ; mouth quadran 

 gular. 

 Length l-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 I am 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. (Madurite? 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. 

 Length less than l-20th, Breadth less than l-20tb , 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 character 



* Established by Capt. Thomas Brown of Edinburgh for some small 

 species found on the coast of Scotland. 



