272 TRANSACTIONS OF THE [May 20, 
DicTrYONEMA FLABELLIFORME Hichwald. Pl. XLIX. figs. 1 and 2 
Note on this species and its associated fauna. 
In the material collected last summer a good many examples 
of a vasiform variety occur. which might pass for var. confertum 
Linrs., but that the hydrothece are closely set as in var Acadi- 
cum ; there are 15 or 17 thecz in the space of 10 millimetres. 
The hydrothece of Dictyonema are about twice as numerous 
in the same space on the branches, as those of most species of 
Bryograptus; they are arranged in a double row, alternating ; if 
we suppose two branches of a Bryograptus joined at the side 
with the cells alternating, a branch similar to that of a Dictyo- 
nema would be produced; owing to its double row of cells Dic- 
tyonema produces a thicker branch than Bryograptus. 
In one or two examples of this species collected by Mr. G. 
van Ingen, there appears to be short rootlets developed from 
the proximal end of the sicula (See Pl. XLIX., figs. 1 and 2). 
These were adult examples, from the horizon 3c, where this 
species is most abundant. It might appear from such examples 
as these, that it would be possible to show the existence of a 
sedentary variety or stage in this species; still, it does not 
seem that this condition of the hydrosome is at all frequent, 
‘for among scores that have been examined since these were 
found, none with roots have been detected. Possibly these pro- 
cesses may have had some other office than that of anchoring 
the hydrosome to the bottom; so far as they are visible they 
are too short to afford more than a very feeble foothold at the 
surface of the soft ooze in which Dictyonema was buried. 
Although we can recognize three different types of Rhabdo- 
pores in the Dictyonema beds (including 3) and ¢), their occur- 
rence is comparatively rare. I suppose with an hundred layers 
bearing in profusion the skeletons of Dictyonema, one would 
occur loaded only with the remains of Rhabdopores, though 
others will be found in which such remains are mixed with and 
masked by the skeletal parts of Dictyonema. Usually the for- 
wer are confusedly crowded together on the layers where they 
they alone occur, and only at rare intervals does a straggler 
from the crowd appear on the surface of a layer with its parts 
so displayed that the plan of structure can be made out. 
So far as numbers are concerned the genus Bryograptus bears 
off the palm among these Rhabdopores, for it exhibits the 
greatest profusion of individuals, but occasionally a mass of the 
little Clonograptus proximatus is found covering the surface of 
a layer. The remains of B. lentus are scarce, and those of B. 
; 
q 
; 
age 
