REPORT ON THE DIATOM ACE^K. 1 1 5 



is marked by many areas or compartments which arc limited by folds or depressed lines, 

 while each compartment is ornamented by a pointor granule — the latter character being one 

 of the chief distinguishing features of the jjenus Stictodiscus. It is true that here no radiat- 

 ing folds occur at the circumference, and that the granules arc more dense at the edge than 

 at the centre ; hence the frustule should probably be designated Slictodiscus quadricornis, 

 although its precise determination must remain somewhat uncertain. 



Professor Cleve, in his communication On Some Rare and Little-Known Diatoms, 1 has 

 described two forms under the name of Triceratium, which, in my opinion, are also true 

 Stictodisci. The first — Triceratium gallapagense, is shown in his plate vi. fig. 72. It is a 

 triangular acute-angled form, with granules sparsely scattered in the middle, but more 

 densely disposed at the sides, where they form short rows, while fine branching lines of 

 more simple points are seen at the angles. In the figure the few radiating lines which 

 are indicated evidently denote the characteristic folds of Slictodiscus. It should accordingly 

 be designated Stictodiscus gallajoagensis. It is distinguished from my Slictodiscus 

 bicoronatus specifically by the absence of the central corona. 



The second form referred to by Cleve as Triceratium margaritiferum (loc. cit., pi. vi. 

 fig. 76) is a coronated Stictodiscus. It has been described by Cleve as follows : — "Valve 

 quadrangular, with concave sides and rounded angles, without processes. Surface probably 

 plane. Structure tolerably coarse, granules arranged near the margins in short lines, 

 smaller in the angles, rare and scattered in the middle." In the centre of the figure there 

 is also seen a small corona of points which has been omitted in the above description. 

 By examining the various figures which I have given of new species of Stictodiscus, the 

 very close affinity of this species of Cleve is at once apparent, although the folded con- 

 dition of the valve in the latter is not evident. Hence this frustule should be named 

 Stictodiscus margaritiferus. 



The above remarks on Stictodiscus and Triceratium were finished when the nineteenth 

 part of Schmidt's Atlas of the Diatomaceae was published. In that work very good 

 figures are given on plate lxxiv. of several new species of Stictodiscus as well as of some 

 already known, and on plates lxxv. and lxxvi. numerous types have been represented as 

 belonging to the genus Triceratium, among which I at once recognised many real 

 polygonal Stictodisci. Among the known discoidal forms Stictodiscus hardmanianus, 

 Grev., is shown on plate lxxiv. fig. 8, in a somewhat small form ; Stictodiscus kit- 

 tonianus, Grev., is seen in figs. 16, 17, and 18 ; while Stictodiscus califomicus, Grev., 

 occurs as fig. 4, and several varieties as figs. 1, 2, 3, 6, 7, and 9. 2 Among the new 

 species, on the other hand, Stictodiscus simplex, A. S., is shown in fig. 11 ; Stictodiscus 



1 Kongl Svensk. Vetensk.-Akad. HandL, Ed. XVIII. No. 5, p. 25, pi. vi. fig. 72.' 



2 These varieties are — Stictodiscus califomicus, Grev., var. areolata, Grun., pi. lxxiv. fig. 1. 



Stictodiscus califomicus, Grev., var. nankoorensis, Grun., pi. lxxiv. figs. 2 and 3. 

 Stictodiscus califomicus, Grev., var. ecostata, Grim., pL lxxiv. tigs. 6 and 7. 

 Stictodiscus califomicus, Grev., pi. lxxiv. fig. 9. 



