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



It possesses the form of a disc with an undulating (almost dodecahedral) margin. A 

 triangle of smaller granules occurs in each of the protuberances, and hence I am of 

 opinion that the frustule originally was discoid, and that its subsequent development did 

 not take place uniformly all round the circumference, but only in a few circumscribed 

 areas. During this process small granules have been formed ; these have gradually 

 increased in size and become disposed in the large regular lines, which occupy the spaces 

 lying between the protuberances. A similar condition obtains more or less markedly at 

 the extremities of triangular frustules, as will be pointed out below. 



Between the lines of the quadrately disposed granules radiating folds arise and extend 

 towards the centre. The compartments circumscribed by these folds are furnished with 

 sparsely arranged granules, and a beautiful corona of smaller points occupies the centre. 



After this frustule had been figured and described I received the nineteenth part 

 of A. Schmidt's Atlas, in which the same form is figured at Plate lxxv. figs. 6 and 7, 

 under the name of Triceratium eulensteinii, Grun. Although therefore recognising the 

 right of precedence of the well-known Austrian microscopist in the case of the specific 

 determination, I cannot accept his generic name, but assign the organisms, for reasons 

 already quoted, to the genus Stictodiscus. The frustule was gathered both in the Sea of 

 Japan and in the Philippine Sea. 



Stictodiscus radfordianus, n. sp. (Plate XVII. fig. 10.) 



Forma octogona, lineis undulatis, et angulis subproductis rotundatis inclusa ; zona 

 regulari ordine quadrato granulata, plicis a margine radiantibus ; granulis medio raris ; 

 puuctulorum corona umbilicali. . In Archipelago Philippinarum. 



This frustule, which is still more elegant than that last referred to, belongs to the 

 coronate section of the genus. It possesses an octagonal form with undulating sides, 

 while the angles are rounded and scarcely elongated. A belt formed of four regular rows 

 of granules runs round the periphery of the valve. These granules are disposed in a 

 quadrate manner, and folds extend between them in a centripetal direction. In the middle 

 region small granules are sparsely disseminated, and the centre is marked by a beautiful 

 corona of small points. Here too, as in the case of Stictodiscus eulensteinii, rows of small 

 granules occur at the angles, and as in the former case seem to indicate points of gradual 

 increase. 



The specific name has been given in honour of Dr Radford, to whom, in part, I am 

 indebted for being invited to examine the Diatoms brought home by the Challenger 

 Expedition. 



II. Radiato-Areolate Forms of Stictodiscus. 



In all these types, folds of greater or less length radiate from the circumference towards 

 the centre, and the central space is subdivided into areoles in a reticulate manner. 



