NOTICE OF THE GENUS TETRAPEDIA, ETC. 363 



from having but three apices, its more projecting but com- 

 paratively less broadly rounded lobes call to mind Reinsch's 

 (unnan^ed) form, fig. 8, Avith its four semicircular lobes, cru- 

 ciately arranged, and Avitb a shallow subacute (instead of a 

 broadly rounded) sinus between them. As before, we might 

 momentarily suppose it possible to deprive one of such forms 

 as fig. 8 of one of its semicircular lobes, and the remainder 

 '^ shoved round " so as to render the now (supposed) but 

 three to become equidistant, still, even apart from the bristles, 

 the forms Avould not be alike, yet, as in the prcA-ious case, the 

 approximation or " affinity" cannot but be regarded as suffi- 

 ciently striking ; and further, my fourth form, this admitted, 

 would seem thus (through such as fig. 8) to be connected 

 even with T. gothica (Reinsch). 



So far, then, as our acquaintance with these little algae here 

 referred to reaches, there appear to exist four (if not five) 

 distinct yet kindred figured " Chroococcaceae" — their re- 

 markable shapes preclude their being regarded as " Lichen- 

 gonidia/' but whether mature plants or stages in the growth 

 of any more complicated structures remains a problem. Ours 

 arc at least forms which here and there recur, and one can at 

 once recognise them as always offering the same character- 

 istics, and as maintaining their apparent individuality. 

 Whether they are '' species'' or not, fit may be a matter of 

 convenience, should observers meet them elsewhere, and be 

 able to throAv a light upon them, to have at least a means of 

 their recognition. For the reasons mentioned, it occurs to 

 me as preferable (at least provisionally and temporarily) to 

 record them under Keinsch's genus, if, indeed, that observer 

 may not consider it unallowable so far to modify the terms 

 thereof as to admit of its embracing the two new forms. It 

 may be objected that the very name of the genus would pre- 

 clude the admission of a three-\o\ied. form into it, but the 

 name Sta\irastrum is retained, though only a minority of the 

 forms referable thereto are cruciate or quadrangular in end- 

 view ; so also, with Triceratium — where four- and five- angled 

 forms occur, and so on. I venture, then, to cast the descrip- 

 tions of these forms as follows : 



Class, Phycochromacese. 



Family, Chroococcaceae. 



Genus, Tetrapedia (Reinsch) mut. quodammodo char. 



Cells compressed, quadrangular, or triangular, equilateral, 

 becoming subdivided into quadrate or cuueate segments or 

 rounded lobes, either by deep vertical or oblique incisions, 

 or by wide angular or rounded sinuses. 



