358 WILLIAM ARCHER. 



whicli; if carried out to the same extent, would result in each 

 of the sixteen segments being cut into four further (tertiary) 

 segments — such a tablet as fig. 6 represents would then 

 become one of sixty-four segments of four times the super- 

 ficial dimensions of the former. Do the segments, at some 

 epoch, and what, become cut through, and such as fig. 1 or 

 3 result ? The words of Reinsch's description convey that 

 this takes place, though he has nothing afterwards explana- 

 tory as to the point. Are the holes a constant characteristic ? 

 or can they point to an impending dislocation or disuniting 

 of the segirients, this initiated, in a singular manner, it is 

 true, at a new place of origin, instead of by a carrying 

 onwards of the vertical incisions ? The foramen or hole, 

 shown in fig. 5, resembles the central interspace of fig. 8, 

 owing to the direction of its angles, but the holes in the com- 

 pound tablet, shoAvn in fig. 6, as before drawn attention to, 

 have the angles in the reverse direction. They are depicted 

 as, and denominated holes, by Reinsch | may they be, after 

 all, but interspaces, and the segments distinct cells, cohering 

 at the adjacent angles by a gelatinous cushion (not united by 

 a narrow isthmus of the cell itself, this afterwards perforated), 

 and thus the opening amounting to no more than a break in 

 the temporarily cemew/my medium ? But if, as we must infer 

 as yet, they are truly openings formed in the " cell " itself, 

 they do not seem to present themselves for some time, appa- 

 rently at least until the primary incisions are advanced ; and 

 the question arises as to how they first originate ? 



Nor, indeed, are queries similar to those suggesting them- 

 selves, touching T. gothica, apparently at all more capable of 

 receiving satisfactory replies, as regards any of the three 

 other forms constituting with it the subject of the present 

 communication. The second form referred to this genus by 

 Reinsch, Tetrapedia Crux-Michaeli, is (like the preceding) 

 very minute, compressed, quadrate, the lateral margins 

 entire, and, in all the examples noticed, with two shallow 

 sinuses or concavities extending from the middle point of each 

 side on to the angles, thus producing an obtuse-angled cen- 

 tral protuberance, the margin at all the four angles deeply 

 and obliquely incised, the incisions reaching to nearly two 

 fifths of the diagonal diameter of the cell, their sides recti- 

 lineal, acute at the inner extremity, slightly widening up- 

 wards (fig. 9). The incisions thus bisect the right angles of 

 the quadrate cell, and subdivide it into four broadly cuneate 

 segments, the outer angles of which are sub-acute, and with 

 the two gentle sinuses, as before referred to, occupying the 

 whole of the outer margin. The edge or side-view of the 



