On Streptelasiiia Frofandam. — Sardeso)i. 28b 
Mcute. The septa, developing from the inner side below tlie 
margin, were mere inward projections of the theca at first. 
The septa extended upward nearly but not quite to the grow^ 
ing margin of the cell. One sees that the exact position of 
the base of each septum is marked in most cases by an exte- 
rior longitudinal furrow in the theca and this proves seeming- 
ly that nearly always the point of the septum proper was pre- 
ceded by an inflection of the calycle margin, corresponding to 
the later position of and continuous with the septum. The 
beginningof the septum proper is not an inflection but a thick- 
ening of the theca and where septa have begun to develop the 
wall is thence dilFerentiated into septa and inteiseptal wall 
(lig. 1, pi. XVII). Evidently' the septa grew rapidly towards 
the axis of the polypite or, in otiier words, in a direction per- 
pendicular to the direction of growth of the calj'cle margin. 
Their growth in thickness was many times slower. Like the 
theca which grew more rapidly at the margin upwards than 
in thickness, so each septum grew rapidl}'' at the margin but 
slowly in thickness. The bases of the septa are seen in cross 
sections of the thickened wall to be fixed wedge-like into the 
theca (figs. I and 2, pi. XVII). There is no fine division be- 
tween theca and septum but a quick transition from darker 
to lighter colored deposit as seen in thin sections. The theca 
is the darker and shows chiefly the concentric striation of the 
organic constituent. The septa show the radiating constitu- 
ent of the mineral constituent, but Nicholson (op. cit.) figures 
what would be the organic striation in these too, probably by 
mistake. 
The theca grows, of course, only on one side, i. e. inwards, 
while the septa thicken on both sides, and, since the septa are 
not far apart, the}' coalesce as a rule laterally not far from 
their bases, excluding the theca so that it fills only the si)ace 
between the septa before they coalesce. This takes place about 
at the ends of the minor sized septa. A sharp demarcation 
remains between the septa when tlie}^ are in contact, because 
the calcareous prisms in one septum meet those of the other 
obliquely. Open spaces intervene under certain conditions 
after and before the septa have once coalesced. A median de- 
marcation within any septum is very rarely observed, but the 
median portion or primary layer is regularly more transparent 
in sections than the later deposited thickening upon it. 
