50 J. W. DAWSON ON THE MICROSCOPIC 
branches of Syringopora and similar corals included in the mass of 
Stromatopora. 
It is evident from the above description that the animal matter 
of Stromatopora must have occupied the chambers or interspaces, 
and must have extended from chamber to chamber through the 
pores and hollow pillars. Such a structure is obviously that of a 
rhizoped rather than of a sponge. Further, the arrangement of the 
laminze and pillars is very nearly allied to that of Parkeria and 
Lofiusia as described by Carpenter and Brady, which I have myself 
studied in specimens kindly given to me by Professor T. R. Jones *. 
In so far as the hollow pillars and perforated plates are concerned, 
it has some points of correspondence, though more remote, with 
Receptaculites. The supposed oscula on which has been based 
a reference of these forms to sponges are certainly not constant. 
I have seen large masses of the form above described, presenting 
more than 30 square inches of surface, without a trace of an oscu- 
lum ; and in those specimens where tubular orifices appeared, I have 
found that they cut like perforations made by a boring instrument 
through the mass, irrespective of its structure, and that they were 
lined with continuous calcareous walls different from the lamine of 
the fossil. It is scarcely necessary to say, after the above descriptions, 
that I attach no scientific value to the ingenious and elaborate attempt 
of Mr. H. J. Carter (‘Annals and Magazine of Natural History,’ 
ser. 4, vol. xix. p. 44) to prove that Stromatopore are skeletons of 
hydroids allied to Hydractinia. The resemblances of Stromatopore to 
these hydroids are altogether superficial, and depend on both having 
a parasitic and concentric habit of growth. In every essential cha- 
racter they differ entirely, and can have no close zoological affinity. 
In comparison with Hozoon, the general appearance and habit of 
growth are so similar that specimens cannot easily be distinguished 
by the naked eye, or where the minute structures are not preserved. 
In microscopic structure the thin lamine of Stromatopore correspond 
to the proper wall of Hozoon. The thickening of the walls corre- 
sponds to the supplemental skeleton, and the horizontal tubes to the 
canals, while the interspaces and the pillars correspond to the 
chambers and connecting walls of the older fossil. ‘The main struc- 
tural difference is, that while Hozoon has a delicately tubulated proper 
wall of Nummuline type, that of Stromatopora has coarser perfora- 
tions and pores. Stromatopora and Hozoon may both be regarded as 
large sessile laminated calcareous Rhizopods; but the former pre- 
sents a less generalized type than the latter, which combines struc- 
tures that were usually separated even in the Paleozoic period. 
Stromatopore of the type above described are abundant in the 
Corniferous Limestone. ‘They occur throughout the Upper Silurian 
and are especially abundant and of large size in the Niagara Lime- 
stone, where they abound even in those Dolomitic beds that contain 
* More recently I have also studied the remarkably beautiful species of 
Loftusia from British Columbia described by Mr. G. M. Dawson, which confirm 
the resemblance of these specimens to Stromatopore (see his paper read before 
this Society, infra, p. 69). 
