BRIGHTWELL, ON TRICERATIUM. 273 



Mr. Shadbolt's T. arcuatum (See 'Trans. Mic. Soc, Vol. 

 II. p. 15, PI, I., fig. 5 ') comes also very near the same species, 

 if it be not identical with it. 



T. comtum ? Ehr. — This species has recently been added 

 to the British Fauna, by Mr. Roper. See ' Mic. Journal,' 

 Vol. II. p. 281. I have in my paper erroneously referred to 

 Klitzing's species Algarum for this species ; but the only notice 

 I find of it is in the last edition of Pritchard's ' Infusoria,' 

 where a description is given, I presume from Ehrenberg, but 

 it is marked doubtful, and 1 perceive by Professor Smith's 

 recently published 2 vol. ' Brit. Diatom,,' he is not satisfied 

 that it is distinct from favus. 



T.favus. — I have lately received a small gathering from 

 Sierra Leone, abounding in this species ; and among the 

 frustules I liave detected two of a cubical or square form, of 

 which 1 have given a figure. This variety is of great interest, 

 as confirming those discovered in two other species of Trice- 

 ratia, described and figured in my former paper. These 

 varieties, and the singular and bizarre forms into which 

 another species hereafter mentioned runs, show a tendency in 

 the frustules of this genus to vary from the regular form. 



In a letter I have received from Professor Bailey, he says, 

 that although he leans to my opinion that these 4 and 5-sided 

 forms may be varieties of the triangular ones, he is not yet 

 fully convinced that this is the case, T.favus is, he says, 

 abundant on their coast, and he has seen it by thousands at 

 least, yet not one 4-sided or 5-sided one occurs ; while in 

 South America, where the same species is equally abundant, 

 a species with 4 sides, which he refers to Amphitetras for the 

 present, occurs with T.favus, and resembles it closely in its 

 markings. The 4-sided forms having now been met with in 

 connection with three distinct species, will, we think, go far 

 to establish them as varieties. The projection of a con- 

 necting membrane beyond the suture of the valve, which is 

 one of the characters of the genus Amphitetras, is not seen in 

 these square forms. 



The fine species discovered by me, and which in my former 

 paper is described as T. striolatum, Ehr., appears to be new ; 

 and my T. membranaceum to be T. striolatum, Ehr. See Mr. 

 Roper's paper ' Mic. Journal,' Vol. II, p. 8, PI. VI., fig, 3. 

 Mr. Roper's description and figure of T. striolatum, Ehr,, 

 will be found to agree with my T. membranaceum, so as to 

 leave no doubt of their being the same. The species described 

 by me in my former paper as T. striolatum, I propose now to 

 call T. formosiim, a name peculiarly applicable to the fine 

 frustules of this large and beautiful species. 



