1896.] MICROSCOPICAL JOURNAL. 139 



Dhufuisionft. — Diameter of tlie pliacold sliell 0.12, of 

 tlie outer in('(liill;irv sliell {).()('>. of the inner 0,03; length 

 of the arms 0.09, bas.-il breadth 0.01), distal breadth 

 O.Of.To. 



Habitat. — Fossil in the rocks of Barbados. 



Note. — On pages .")9 and (JO of the Jouk^al for February are described 

 and illnslrated iwo new species. Figure 1 is Khopalastrum anomalnm and 

 Figure 2 shows Pentin.ostruni irregiilare. From the position of the figures, 

 one might infer the opposite to he the case. Hence attention is hereby 

 called to it. 



On Distinguishing Minerals. 



BY MELVILLE AT WOOD. 

 [Report of paper read before the San Francisco Microscopical Society.] 



Many years ago he had found considerable difficulty 

 in determining', Avitli any degree of aceuracy, the hard- 

 ness of minerals, the scale of hardness then in use, and 

 probably still at many colleges, being a small 1)0X con- 

 taining sami)les of the different minerals and a penknife. 

 The knife was seldom hard enough to scratch wolfram, 

 rei)resentiiig 5 in the scale. To the prospector or miner 

 it is of the greatest importance to be able by some means 

 to determine the degree of hardness. Many fragments 

 of corundum and quartz have been sent long distances 

 to have them determined, the sender thinking them dia- 

 monds. 



^Ir. Atwood had found, after many trials, the easiest 

 mode of determining hardness was to have the minerals 

 representing the various degrees mounted something 

 like a writing diamond. For this purpose you break the 

 corundum, topaz, etc., into small fragments, and after se- 

 lecting those with fine, sharp points, proceed to mount 

 them in the following manner: Take a small rubber- 

 tipped pencil and extract the rubber from it. Then with 



