Triceratium bicorne Cleve
There has been considerable confusion about this species, and it is often subsumed into Triceratium dubium Brightwell, which has a very similar construction but is mostly 6-sided. This confusion is a common situation in the phenotypic taxonomy of the genus, and there is no consensus as to the genus or species limits of many taxa within the family Triceratiaceae.
The valves of T. bicorne are quadrate (Fig. 1, SEM) with ocelli at two of the corners and external tubes of the rimoportulae at the other two corners (Fig. 1 and Fig. 2, SEM detail of Fig. 1, arrow). The valve surface is slightly convex and composed of pseudoloculi enclosing clusters of areolae that are more or less radially arranged. Minute spines are scattered over the pseudoloculus walls (Fig. 2). These features are shared with T. dubium (Fernandes et al. 2001). Although it seems rational to include T. bicorne with T. dubium, a recent study has documented distinct genetic differences between the two (Ashworth et al. 2013; MP Ashworth, personal communication, 9 Feb 2015).
Because T. bicorne was only seen once, nothing can be said about its distribution and abundance; it is clearly a rare species. It would be useful to look at morphological variation within a population to discern phenotypic support (e.g. Cox 2014) for genetic distance between the two similar species.