MEMORANDA. 105 



Length -0040" to -0045" of an inch ; strise 50 to 55 in 

 •001.'' 



I enclose a drawing magnified 400 diameters. 



Pleurosigma Parkerii. 



Valve broadly lanceolate, acute extremities produced, 

 flexure considerable ; colour pale yellow. Length of valve 

 •0038" to "0040" ; transverse strise "0060 ', and stronger than 

 the longitudinal. Fresh water. Thornton-le-Moor, Lincoln- 

 shire, Mr. W. Parker. 



