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



This small disciform valve lias some affinity to Coscinodiscus denticulatus (Plate III. 

 fig. 8), inasmuch as its surface is, like that of the latter, sparsely covered with spines 

 or denticules. Its granulation, however, instead of being disposed in a radiating manner, 

 presents no distinct order, while its margin is not striated, but plain. The two frustules 

 also differ greatly in point of size, and their specific values cannot be doubted. 



Coscinodiscus atlanticus, n. sp. (Plate V. fig. 8.) 



Cellulis aequalibus fasciculatim radiautibus a margine ad medium radii, in centro 

 autem inordinate dispositis. In mari Atlantico meridionali. 



In this elegant disc the radiating lines of granules are disposed in fascicules around 

 the margin, but the arrangement in the central part is irregular and more or less lax. As 

 the character of the granulation is of the greatest importance in the determination of the 

 species of the present genus, the specific value of the valve now before us is at once 

 obvious. It was collected in the South Atlantic. 



Coscinodiscus atlanticus (?) n. sp., var. nov. (Plate III. fig. 7.) 



The valve here represented differs from the typical specimen of Coscinodiscus atlan- 

 ticus in the following respects: — (1.) The part occupied by the radiating fasciculately 

 disposed lines of granules is considerably greater than that ornamented by irregularly 

 arranged granules ; and (2.) the sculpturing passes into the condition of very debcate 

 striation at the margin, where a well-marked rins; of considerable breadth occurs. As 

 it is not possible to determine the precise importance of these distinctions, I regard the 

 present form provisionally as a variety. 



Coscinodiscus stellaris, Roper, var. fasciculata, nov. (Plate V. fig. 9.) 



The valve here represented was obtained near the ice-barrier of the Antarctic, and 

 must be regarded as a variety of Coscinodiscus stellaris, Roper. It is distinguished from 

 the latter by its very delicate fasciculated granulation — a circumstance which is not men- 

 tioned by Roper in the case of his typical species, nor indicated in the figure given by 

 that observer, and reproduced by Pritchard (see page 155). 



Coscinodiscus (?) pacificus, n. sp. (Plate VIII. fig. 5 ; and Plate XXII. fig. 1.) 



Valvis cellulosis ; cellulis subhexagonalibus, insequalibus ; margine late striate In 

 mari Pacifico. 



The valves here shown are ornamented with large subhexagonal cellules, and each pos- 

 sesses a wide striated border, which serves to recall the genus Endictya of Ehrenberg. 1 

 Whether they must be ascribed to the latter genus, however, cannot be determined till 



1 Ehrenberg, Mikrogeologie, pi. xxxv. A 18, figs. 6 and 7; Pritchard, op. cit., p. 831, pi. v. fig. 70.* 



