120 THE VOYAGE OF H.M.S. CHALLENGER. 



observed that the reticulated central space is almost destitute of granules. This variety, 

 like the previous one, was collected in the neighbourhood of the Philippine Islands. 



Stictodiscus reticulatus, n. sp. (Plate I. fig. 8.) 



Liueis granulorum plerumque per plicas a margine radiantes distinctis ; hinc plicae 

 reticulatim distribuuntur ; arese centrales grandiusculae, pluribus granulis plerumque 

 instructas. Ad Zebu. 



This disc is ornamented with lines of granules which are for the most part double. 

 These lines are separated by folds which soon become reticulated after leaving the margin. 

 The meshes of the well-marked somewhat irresrular network thus formed are adorned with 



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more or fewer granules, disposed in small groups. The frustule was obtained at Zebu. 



Stictodiscus margaritaceus, n. sp. (Plate XVII. fig. 12.) 



Disciformis, granulis plerumque magnis, medio raris, ad marginem frequentioribus, et 

 subregulariter dispositis ; plicis a granulo marginali exeuntibus et granulorum lineas 

 discriminantibus. Ad insulas Philippinas. 



In this specimen the granules are unusually large and pearl-like. They are sparsely 

 scattered in the centre and more closely near the margin, where they are divided by slight 

 folds, each of which originates in a well-marked marginal point. The disposition and 

 size of the granules are inconstant. 



III. Triangular or Polygonal Forms of Stictodiscus. 



Stictodiscus varians, n. sp. (Plate XVII. fig. 7.) 



Forma subquadrata, lateribus convexis ; granulis a margine radiautibus, medio rari- 

 oribus et irregulariter distributis ; linese marginales plicis evanescentibus dividuntur. In 

 mari Siuensi. 



This specimen is, in form, transitional between the round and the polygonal types. 

 The discoidal valve tends to become angulated at four points in such a manner that by a 

 further extension of the angulation the round form would become quadrate. The disposi- 

 tion of the granules is regular and somewhat dense at the circumference, but rare and 

 irregular at the centre. At the perimeter the lines of radiating granules are intersected 

 by folds, which soon disappear. The specific name which has been applied is intended to 

 recall the tendency to vary in form from round to quadrate which is exhibited by this 

 interesting Diatom. 



Stictodiscus bicoronatus, n. sp. (Plate VI. fig. 5.) 



Trigonus, lateribus subconvexis et apicibus rotundatis ; zona granulis raris et decus- 

 satim dispositis; granulis medio nullo certo ordine distributis; centrum duplici punctulorum 

 corona insiguitur ; ad apices multipla? punctulorum linese radiantes. Ad oras Japonicas. 



