REPOET_ON^THE DIATOM ACEiE. 117 



This elegant disc is ornamented at the margin with sparsely disposed lines of 

 granules. These become irregular towards the centre, and are replaced there by an 

 irregular corona of small points. The presence of this corona has induced me to include 

 this frustule among the Stictodisci, although the folded condition of the valve, which is 

 the principal generic character, could not be distinguished. It is to be noted, however, 

 that in the different species the folds are found more or less clearly defined, and when 

 they are very slight they become almost invisible, so that the impossibility of recognising 

 them here is not necessarily opposed to the determination that has been arrived at. 



Sticto discus radiatus, n. sp. (Plate I. fig. 1.) 



Granulis in lineas radiantes plicis divisas distributis ; plicis ad centrum evanes- 

 centibus ; centrum granulis caret. Ad Zebu ex insulis Philippinis. 



This frustule, and its variety shown in Plate I. fig. 3, belong to the radiate section of 

 the genus Stictodiscus. They are closely related to the Stictodiscus californicus of 

 Greville, 1 which in its turn is akin to Stictodiscus johnsonianus, Grev., 2 differing from it 

 in the indistinct and shorter radii, and in the condition of the peripheral zone from which 

 these radii spring. This zone is marked in Stictodiscus johnsonianus by a series of round 

 or somewhat elliptical granules which are situated opposite the peripheral ends of the radii, 

 while in Stictodiscus californicus it bears semi-elliptical areolae which usually alternate 

 with the radii. In the forms now under examination, on the contrary, the radii are 

 notably long and the centre always remains free from granules, while the great number of 

 the radii — although by itself a character of no great significance — cannot be overlooked. 



Although the type-specimen shown in Plate I. fig. 1 bears a great resemblance to its 

 variety seen in fig. 3 there are some differences which must be noted. Thus in addition 

 to the greater number of granules which are radially disposed and ornament the valves in 

 fig. 3, there is also present here a somewhat prominent granule at the extremity of each 

 fold, and the radii begin with two small granules. In the course of the radii each granule 

 is elevated upon a subrectangular areola. Much importance cannot be attached to the 

 granules at the extremities of the folds, as their existence is doubtful in some cases — 

 similar appearances often occurring at the margin of the valve in changing the focal 

 distance. The subdivision of the radii into compartments serves to indicate the connec- 

 tion between the radiate and radiato-areolate forms of Stictodiscus. The following 

 definition may be given of the varietal frustule : — " Lineis crebriusculis granulorum in 

 areas rectangulares, granulum in margine ad ortum cujusque plicse. Ad oras Japonicas." 



Stictodictus eulensteirdi, Cstr. (Plate I. fig. 7.) 



Triceratium eulensteinii, Gran., A. Schmidt's Atlas, pL lxxv. figs. 6 and 7.] 

 In Plate I. fig. 7 there is represented an exceedingly elegant form of Stictodiscus. 

 which indicates the transition from the discoidal to the triangular and polygonal types. 



1 Schmidt's Atlas, pi. lxiv. fig. 4. - Micr. Joum., n. s., vol. i. p. 41, pi. iv. tig. 3. 



