298 A. A. MERLIN ON THE MINUTE STRUCTURE OF SOME DIATOMACE^. 



secondaries with equal certainty or distinctness, as I should 

 imagine would he the case were they ghosts formed by the 

 primaries. 



Explanation of Plate 17. 



(All the Jifiures have been drawn under \tk-\nch Zeus cqwehromat.^ 



Fig. 1 . Areolation of a Bidchdphia {reticulata Roper ?). Secondary 



structure of outer cap. 

 Fig. 2. The same, showing structure on the inner plate. 

 Fig. 3. Central portion of Namcula 'prmtQxta valve, exhibiting 



fine secondaries. One specimen unmistakably shows 



the ends of the raphe pipes joined by a finer tube as 



figured. Other specimens only yield faint indications 



of this connection. 

 Fig. 4. Central portion of Navicula lyra^ showing apparent 



secondary structure on the hyaline bands. 

 Fig. .5. Fractured edge of a Pleurosigma formosum, exhibiting a 



projecting row of five "black dots," three of which 



have been partly carried away. 

 Fig. 6. Process of a large Auliscus (OamaimensisX) with fine 



structure resembling that of the A. sculptus. 

 Fig. 7. Large rod-shaped primaries of an Orthoneis valve, each 



constricted centrally and biidged by a broad silex bar. 



Jovrn. Qv.fhtf Mlcro!<copicol Clv.h, Ser. 2, Vol. VJL, No. 46. April 1900. 



