Photographs of Broken Diatom Valves. By Dr. J. D. Cox. 857 



Exposure 12 minutes and plate afterwards intensified with mere, 

 bi-cblor. 



No. 23. Another specimen of same, showing group of large 

 central cells with dotted film, x 1600, exposure 14 minutes. 



No. 24. Navicida granuJaia Brebisson. x 950, exposure 



9 minutes. Showing several fractures through the dots. From 

 H. L. Smith's species typica in balsam. 



No. 25. Odontocliscus suhtilis Ehr. x 1100, exposure 

 14 minutes. Showing crack nearly parallel to the rim and running 

 through the dots. From the same shde as No. 11. 



No. 26. Trieeratium favus Ehr. x 1333, exposure 10 

 minutes. A fragment showing film with radiating dots over the 

 large hexagons. Dense medium (2 "4). Same slide as No. 10. 



No. 27. Actinoptychus Ileliopelta Grunow. x 940, exposure 

 7 minutes. Showing finely dotted film extending far beyond the 

 large hexagons, and the fracture through the fine dots. From 

 Peticolas' balsam mount of Calvert Co. earth (Maryland). 



No. 28. Coscinodiscus ocnlus-iridis Ehr. x 900, exposure 

 7 minutes. A fragment of the inner film, showing the "eye- 

 spots." From same slide as the last. 



No. 29. Same as 28 with slightly difi'erent focus. 



No. 31. Finnularia major W. Sm. x 870, exposure 

 6^ minutes. Showing costfe standing out like the teeth of a comb, 

 the thin connecting film being mostly removed. From H. L. 

 Smith's slide of Nav. rliomhoides in dense medium (2-4). 



No. 35. Navicula granidata Breb. x 1000, exposure 

 5^ minutes. Showing fractured margin, the break being through 

 the dots. From H. L. Smith's species tijpica, dry. 



No. 38. Navicida seria7is Kutz. X 1130, exposure 10 minutes. 

 Showing fracture through the dots. From Moller's balsam mount 

 of Monmouth earth (Maine). 



No. 39. Pleurosigma angidatum W. Sm. x 1250, exposure 

 13 minutes. Showing marginal fracture through the dots. From 

 Peticolas' balsam mount of Calvert Co. earth (Maryland). 



No. 41. Mastogloia angidata Grunow. X 1015, exposure 



10 minutes. Showing segment broken out with fracture through 

 the dots and along the median line. From Peticolas' balsam mount 

 of diatoms from Long Island Sound. 



No. 44. Same species, x 1040, exposure 6 minutes. The 

 septum separated from the valves. From Peticolas' dry mount of 

 diatoms from Long Island Sound. 



No. 46. Pleurosigma angulatum W. Sm. x 1250, exposure 

 7J^ minutes. Showing marginal fracture through dots, and same 

 on the surface where the shell has been crushed. From Peticolas' 

 dry mount of Nottingham earth (Maryland). 



No. 47. Coscinodiscus suhtilis Ehr. var. molaris C. X 1130, 



Ser. 2.— Vol. IV. 3 L 



