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



near the coast of South America. Between Coscinodiscus craspedodiscus, O'Me. — which 

 is represented on Plate III. fig. 5, and in which the areolation corresponds exactly to 

 that of the original except in the case of the margin, where the details could not be 

 adequately pourtrayed — and the present frustule there is no risk of confusion, while the 

 latter may be distinguished from Coscinodiscus arafurensis, O'Me., 1 in the following 

 respects : — (1.) It is of smaller size ; (2.) its radiating rows of cellules regularly diminish 

 from the circumference to the centre, where there is (3.) a smooth area somewhat smaller 

 than that of Coscinodiscus craspedodiscus, and terminated less irregularly than that of 

 Coscinodiscus arafurensis. Notwithstanding, however, the difference in size, in the char- 

 acter of the areolation, and in the condition of the central areola, I am of opinion that we 

 are here dealing with nothing more than a variety of O'Meara's typical species. 



Coscinodiscus mirificus, n. sp. (Plate III. fig. 6.) 



E maximis ; granulorum lineis, radiautibus ; area centrali, irregulari, grandiuscula ; 

 cellulae punctulorum lineis circumducuntur. Diametrum = 326 m. Ad Hong-Kong in 

 mari Sinensi. 



This singular species is closely allied to the above-mentioned Coscinodiscus arafurensis, 

 O'Me. Its diameter is 326 m., and its large central areola has a very irregular outline. 

 The granulation is radiating, but the granules are at the same time disposed in exceutric 

 curves which resemble the guilloche of a watch. When examined with a homogenous 

 immersion lens and accurately adjusted light each cellule or areole is found to be bounded by 

 a hexagonal margin of extremely minute punctiform granules (Plate III. fig. 6 a). This 

 curious frustule is from the neighbourhood of Hong-Kong. 



Coscinodiscus papuanus, n. sp. (Plate III. fig. 3.) 



E maximis ; granulis minimis radianter per nonnullas lineas distinctions in totidem 

 denticulos submarginales exeuntes divisis ; centrum nonnullis rarioribus granulis notatur. 

 Diametrum = 152 /x. In mari Arafura. 



This large disc (152 /m. in diameter) is covered with radiating lines of small granules. 

 These are separated by rows of very minute granules which pass centripetally from as 

 many submarginal points or denticules, but disappear towards the centre. Here a few 

 less crowded granules occur, and this circumstance serves to distinguish the present form 



1 The original observations published on Coscinodiscus arafurensis, O'Me., are as follows : " The form is 

 large, diam. O015", however, considerably smaller than the very striking species exhibited ... by Mr. O'Meara 

 under the name of Coscinodiscus craspedodiscus, a comparison with the leading features of which would best 

 pourtray the characteristics of the present. Here the broad margin so remarkable in the former is absent. In 

 the present form as in it the radiate lines of areoles terminate some distance from the centre ; the central blank 

 space, however, is rrmch smaller, and the lines of areoles are of more equal length. Areoles of margin sub- 

 hexagonal, diminishing in size towards the ends ; they are shorter, broader, and much more robust than in 

 Coscinodiscus craspedodiscus." — Quart. Journ. Micr. Set., vol. xvii. p. 463. 



