62 THE VOYAGE OF H.M.S. CHALLENGES. 



Campylodiscus, Ehrenb., Men. 



As constituted by Ehrenberg and Meneghini, this genus embraced rotundo-elliptical 

 forms with subradiate costules and canaliculi. By a greater development at the periphery 

 than at the centre the frustule assumes a slightly tortuous aspect, and as this continues, 

 the general aspect becomes more or less deeply curved, so as finally to resemble a saddle. 

 The definition of the genus has been given by Pritchard 1 in the following words : — " Valves 

 equidistant, frustules solitary, disciform ; disc tortuous or saddle-shaped, rotundato-elliptic, 

 costate, costse mostly radiate." 



The tortuous form of the frustules renders it difficult to obtain correct figures of them, 

 particularly from their zonal aspects. 



In this genus, as in Surirella, the valves are surrounded by elegant submarginal 

 wings, which become elevated on parting from the zone or girdle, a circumstance which 

 has caused difficulty in the determination of species. 



Campylodiscus japonicus, n. sp. (Plate XL fig. 1.) 



Forma subrotunda, grandis, costularum vel potius canaliculorum brevium circulo 

 numeroso (fere 80) marginali cincta ; costulse vel canaliculi a lineis spinulosis disseptse, 

 quse dein evanescunt ; area hyalina centralis subrotunda. In mari Japonico. 



This Diatom possesses the form of a large disc with a number of short radial costules 

 or canaliculi. These are separated by lines of short " thorns," which occur on the connect- 

 ing zone, and run centripetally from the extreme margin. There is also present a hyaline 

 central subrotund area, which approximately coincides in shape with that of the entire 

 frustule. The specimen was collected in the Sea of Japan. 



Campylodiscus zebuanus, n. sp. (Plate XL fig. 10.) 



Forma mediocris subrotunda, costis ab area lineari axiali hinc inde radiantibus, medio 

 angulariter curvatis. Ad Zebu, in mari Philippinarum. 



This moderately large frustule was collected in the neighbourhood of Zebu in the 

 Philippine Sea. It possesses a rounded outline and a smooth narrow almost linear central 

 area, which runs along its axis. From the margin of this area radial costules run across 

 the surface of the valve, and are folded alon^ a line almost concentric with the ed^e. 

 The two extremities of the central area terminate at two points, which may be called the 

 poles of the frustule, and they seem to indicate two centres of development for the valve, 

 as structures which appear to be rudimentary costules are perceptible in these regions. 

 It is worthy of remark that when the developmental significance of these two points is 

 recognised it is easy to understand how the valve may become more and more winding 

 and ephippiform. 



1 Op. cit, p. 798. 



