NOTICE OF THE GENUS TETRAPEDIAj ETC. 357 



both walls, the membrane from both sides lining them thus 

 making a free passage through the thickness of the cell. 

 They are not, if we judge Reinsch's figure aright, comparable 

 to the openings in the *' coenobium " of a Cojlastrum, or a 

 Pediastrum, or of Gonium, &c., Avhich are the spaces between 

 the component individualised cells of a stratum, but here it 

 Avould appear that even the tablet, shown in fig. 6, is still 

 only one ce//, with sixteen compartments, nearly, but not quite, 

 shut off from one another, and therefore still in mutual inter- 

 communication. Repeatedly vertically quadripartite is thus 

 the main feature of this form. 



One of Reinsch's figures seems to offer a deviation from 

 the general description here sought to be conveyed (fig. 8), 

 Four apparently distinct cells are closely juxtaposed, the in- 

 dividual cells (instead of quadrate, the angles rectangular, 

 but, as mentioned, rounded off) are here equally four-lobed, 

 the lobes semicircular and entire. Thus, between the four 

 lobes occur four sinuses, these acute-angled at the deepest 

 point. In the centre, between the whole four cells, there 

 occurs an acutely quadrangular hollow-sided vacant interval 

 of equivalent length and breadth, and between each pair of 

 the four-lobed cells also an acutely quadrangular hollow-sided 

 vacant interval, longer than broad, the longer diameter of 

 these four interspaces running in the direction of the angles 

 of the equally quadrate central vacant interval — the form and 

 direction of these {five) interspaces being, of course, simply 

 due to the semicircular outlines of the lobes of the juxtaposed 

 cells. One can, in fact, exactly reproduce the outline pre- 

 sented by the form in question, and even bring out the whole 

 of the characteristics of the contour of fig. 8, by placing six- 

 teen similar coins in four groups of four each, the coins so 

 much overlapping one another as to allow, as nearly as 

 possible, just one half the circumference of each to remain 

 uncovered. Of this form Reinsch has seen but a single 

 specimen, and, referring to it as he does only in the descrip- 

 tion of the plate, is disposed to take it for a distinct plant. 



Such (with this aberrant, or more likely quite distinct 

 form) is this interesting chroococcoid, T. gothica (Reinsch), 

 so far as we are able to gather from the material aff'orded. 

 The question is, what is its mature state ? Do any portions, 

 more densely filled with contents, become shut off", as resting- 

 cells or " spores " (such as in Anabaina) ? What limit is 

 there to this subdivision ? Figure 6, with its sixteen-quad- 

 rate segments, offers at all the sides of all the segments the 

 same minute central emargination as in the earlier conditions, 

 indicative (?) of a further formation of similar incisions^ 



