RiANN — DIATOMS OF THE ALBATBOSS VOYAGES. 289 



TRIGONIUM Cleve. 



jcmium Cleve, Ofv. Kgl. Vet. Akad. 24: 663. L868; Bih. Sv. Vet. Akad. Handl. 



1": s. L8 



7 Iceratium Ehrenb. err. det. Bail. Smithson. Contr. K n< »w 1 . ii : 1851. 



Bright. Quart. Journ. Micr. Sci. 4: 275. pi. 17. f. 16. It 



B;>i<hil r L;<, Gray, in pari; Bright. Quart. Journ. Micr. Sci. 7: 181. pi. 9./. 15. L859. 



Zygoceros Ehrenb. in part; Bail. Smithson. Contr. Knowl. 7: 11. pi. 1. 



Amphitetras Ehrenb. in pan: De Toni, Syll. Alg. 2: '.too. L894. 



Ampkipentas Ehrenb. in part; De Toni, Syll. Alg. 2: 911. L894. 



Nothoceratium !>•• Toni, Syll. Alg. 2: '.Ml. L894, in part. 



lodiscus Grev. in part; Grun. in Van Heur. Synop. j>1. 126. f. / .'. L881. 



Pseudotriceratium Grun. Denkschr. Akad. Wien 48 2 : I 



Tin- genus Triceratium a- constituted by Ehrenberga included simply triangular 

 specimens i<\ the genua Biddulphia Gray. The striking bul inconstant characteristic 

 led him to Belecl the very descriptive name and to word hi.- diagnosis so a- to convey 

 this one idea. Hi- type species, T. favus, agrees with this. I' i-. therei 

 on a wholly untenable conception and i- a synonym of Biddulphia. Gradually, 

 however, it underwenl modification chiefly at the hands oi Brightwell& and Kali'-.' 

 whereby it came to include form- with more than throe horns, together with a I 

 forms where On' horns at the angles are obscure or wanting, in fact, almost anything 

 of a polygonal character, when seen from the valval side. Jt tints came aboul that 

 the genus grew to be a mixture of many genera, whose Bole bond of union was the 

 worthless accident of L) more or less angular valve outline. Tim- polygonal specimens 

 of Stictodiscus Grev., of DitylumBail., of the triangular form- of Hemiaulus Ehrenb., 

 which make tip Heiberg's invalid genus Trinacria, of the triangular forms of Terpsi- 

 noe Ehrenb., which Wallich calls Hydrosera, and others found a resting place in 

 this unscientific medley. De Toni d performs the useless task of restoring it to its 

 original boundaries, except that he excludes those triangular forms represented by 

 Greville's newer genus Entogonia. It is evident that Triceratium Ehrenb. repr< 

 nothing but a peculiar configuration of Biddulphia: nor have the attempts to recon- 

 Btruct it resulted in anything but confusion. It must, therefore, ho abandoned, a 

 course adopted by Van Heurck, Boyer, and others. But in doing this some diatoms 

 now bearing the name Triceratium remain which can not ho referred to any of the 

 before-mentioned genera. This ha- led to the necessity of a genus for these form.-: 

 and I have placed them in the genus created by Cleve for this pur])"--. Be defines 

 it as follows: "Hufvudytan triangular, sidoytan rektangelformig utan frain.-prii _ 

 utskott eller horn.'* It i> true that this i- too indefinite, as it would include such tri- 

 angular and quadrangular forms as we meet with in Stictodiscus, as well as the mem- 

 bers of the genus Entogonia, a genus thai Cleve recognizes a- distinct; and further 

 would exclude the occasional biangular or fusiform specimens of —mo species nor- 

 mally triangular. But that the latter are not intended to be excluded byCleve is 

 shown hy the fact that in discussing Trigonium arcticum (Bright. Cleve ehe speaks 

 of the biangular variety known a- / i Ehrenb. 1> rs the 



members of Triceratium (exclusive of those referred to ..tier established genera, as 

 Stictodiscus and Hemiaulus to Biddulphia, whether the angles are surmounted by 

 horn-like processes or not, and to agreal extent Van Heurck does the same. This 

 takes from Biddulphia its most Balienl characteristic and places in the genus such 



« Phys.Abh. Akad. Wise. Berl. 1839: 129, 159. L841. 



b Quart. Journ. Micr. Sci. 1: 215. L8 



- Pritch. lli-t. [nfus. ed. I. 853. ; 



d Do Toni, Xotari-ia 5: 912. L890; Syll. Alg. 2: 917. L894. 



eBih. Sv. Vet. Akad. Handl. 1 : : B. L873. 



/Proc. Acad. Phila. 1900: 1'JUl. 



