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



cave, and its marginal portion notably convex. The central area is ornamented with 

 round radiating granules, while the broad margin has these arranged in a decussate 

 manner. From the border of the central concave part there extends to the peripheral 

 rin<r a series of eleven strongly marked radiating areas, which are raised above the plane 

 of the valve. 



Although this singular valve differs from any of the other specific forms of Cestodiscus, 

 its characters still coincide with those expressed in the definition of this genus as given by 

 Greville. By the use of extremely oblique light, and the homogeneous immersion objec- 

 tive of Zeiss, I have been able to recognise that the long elevated areas project hori- 

 zontally from their origin, and separate afterwards like the talons of a bird of prey — an 

 observation which has suggested the specific name that has been applied to this inte- 

 resting form. 



Eupodiscus, Ehrenb. 



While Pritchard, in his History of Infusoria (p. 842), notifies the characteristics 

 of this genus, which is especially distinguished by the processes disposed around its 

 valves, he very justly observes that the genus A ctinocyclus of Ehrenberg is probably iden- 

 tical with Eupodiscus, and that therefore it is wrong to ascribe the former to the Coscinodisci. 

 The only notable difference between Actinocyclus and Eupodiscus consists in the number 

 of the pseudo-noduli or submarginal processes, of which only one occurs in the former, 

 while two or more are to be found in the latter. 



In the Challenger Collection Eupodiscus jonesianus, Grev., is pretty frequent, having 

 been collected in several localities, such as the Sea of Japan, at Hong-Kong, in the Arafura 

 Sea, in the Southern Ocean between Kerguelen and Heard Islands, and elsewhere. At 

 first, however, it is difficult to determine this Diatom specifically. Notwithstanding the 

 well-known facility which Greville possessed of drawing the most delicate and elegant 

 diatomaceous frustules, his figure of this species does not agree sufficiently exactly with 

 its natural appearance. This will be at once admitted when a comparison is made between 

 plate ii. fig. 3 of the Transactions of the Microscopical Society of London, vol. x., new 

 series, 1862, and the description which Greville himself gives at page 22 of the same 

 volume. This description, however, perfectly coincides with the valves collected by the 

 Challenger, but it is necessary to remark that among the many specimens in my possession 

 not one is furnished with more than two submarginal processes, while these are disposed 

 as if the periphery were tripartite, the place of the third process remaining vacant. 



Eupodiscus insutus, n. sp. (Plate XIX. fig. 6.) 



Disciformis ; tribus processibus submarginalibus munitus ; valvis areolatis et radi- 

 anter punctulatis ; areolis grandiusculis, subrotundis, rariusculis. In Oceano Atlantico 

 meridionali. 



