858 Transactions of the Society. 



exposure 10 minutes. Showing crack through the dots. From 

 Peticolas' balsam mount of Eichmond earth (Virginia) . 



No. 50. Same as 46, x 1350, exposure 10 minutes and plate 

 afterwards intensified with mere, bi-chlor. 



No. 51. Mastogloia angulata, Grunow. X 1314, exposure 

 8 minutes and plate afterwards intensified. One side broken away, 

 showing fracture through dots. From Peticolas' dry mount of 

 diatoms from Long Island Sound. 



