SYSTEMATIC ACCOUNT 283 



Subfamily TRICERATIOIDEAE 



Genus Triceratium Ehrenberg 

 Ehrenberg, 1840 a 



The genus Triceratium has been attacked by many workers from time to time, but 

 little success has attended their labours. In the main they have followed Van Heurck in 

 condemning the genus upon the grounds that it is a collection of forms that are but 

 triangular configurations of the genus Biddidphia. While it must be admitted that many 

 species of Triceratium should be referred to Biddidphia, I can see no reason for allowing 

 the whole genus to fall into synonymy because I recognize in the type species certain 

 fundamental characters which separate it most definitely from all allied genera. 



The genus was established in 1840, two species were described, Triceratium favus and 

 T. striolatum, and the former is usually considered as the type. T. favus possesses poly- 

 gonal valves ; varieties possessing seven or eight sides have been found, but the type is 

 triangular. The sides of the cell are usually straight, sometimes very slightly convex. 

 The angles are furnished with a stout cornutate process. The valve surface is covered 

 with a regular hexagonal loculation. The loculi are usually open upon the outer surface, 

 while the lower wall or floor is furnished with poroids. The valve mantle is narrow. 

 The girdle is always simple and finely punctate. Small spines are usually present on 

 the valve surface at the point of confluence of the walls of the loculi ; these are often 

 developed at the margin of the valve and have the appearance of a palisade. 



The complex structure of the valve is profoundly different from anything observed 

 in the genus Biddidphia. This structure has been ably portrayed by Muller (1871) and 

 Flogel (1884) and separates the genus Triceratium most clearly from all allied genera, and 

 allows the species to be recognized instantly. Based upon this characteristic structure 

 the genus Triceratium is a small, sharply defined group of highly evolved diatoms con- 

 taining about twenty-seven species and varieties. The genus is a littoral one, and the 

 species are solitary in habit. The geographical distribution is somewhat difficult to 

 define, but may be said to be temperate to tropical. 



Triceratium favus Ehrenberg. (PI. X, figs. 2, 3.) 



Ehrenberg, 1840a, p. 79 (159), pi. 4, fig. 10. 



Hustedt, 1930, p. 798, figs. 462, 463. 



Triceratium comptum Ehrenberg, 1844, p. 166. 



Triceratium muricatum Brightwell, 1853, vol. 1, p. 249, pi. 4, fig. 5. 



Triceratium fimbriatiim Wallich, 1858, p. 247, pi. 12, figs. 4-9. 



Triceratium scitulum Schmidt, 1885, pi. 83, fig. 11-16. 



Triceratium sarcophagus Castracane, 1886, pi. 6, fig. 3. 



Triceratium ferox Castracane, 1886, p. 107, pi. 6, fig. 4. 



Biddidphia favus (Ehrenberg) Van Heurck, 1881, pi. 107, figs. 1-4, 1896, p. 475, pi. 21, fig. 643. 



Cells triangular in valve view, almost rectangular in girdle view. Surface of valve 

 covered with regular hexagonal cellulation arranged in straight lines. Angles of the 

 valve furnished with stout cornutate processes. Valve mantle narrow, not constricted. 

 Valve surface often covered with small spines placed upon the walls of the loculi at the 



