MINUTE STKrCTURE OF STROMATOPOEA AND ITS ALLIES. 241 



hints, do not yet afford all that is desirable to unravel the knotty 

 point. It is possible, though, that his future investigations of 

 the ample material brought home may supply facts bearing more 

 directly on the skeletal structure of the fossil Stromatoporoids. 

 Lastly, respecting Sponge alliance, we are beset by obstacles, for 

 neither do the Horny, Siliceous, nor Calcareous divisions, recent 

 or fossil, so far as present knowledge extends, supply us with 

 stable data whereon to assert identity. By reason of the nature of 

 the skeletal basis, the two former groups are necessarily excluded ; 

 while total absence of spicules in the StromatoporcE, as widely 

 understood, renders it impossible to class them unconditionally 

 w4th the Calcareous order of the Sponges. But seeing that 

 Hydrozoa Iconstruction, with its tubular zooidal cavities, tabulae, 

 &c., has not been shown to exist in the typical forms of the Stro- 

 matoporoids, and that neither in Millepora nor Hydractinia &c., 

 so far as we are aware, does such a system of intercommunicating 

 passages and occasionally lacunae without walls obtain, as exem- 

 plified in Stromatocerium &c., we are constrained to adopt the 

 parallel of the Siliceous sponges with fused and adnate spicules, 

 and assume the existence in times past of a Calcareous group 

 of the class Spongida with a continuous skeleton composed of 

 non-spicular granular calcareous matter. We are, however, by 

 no means prejudiced, but hold ourselves open to conviction ; for 

 if hereafter it be demonstrated that the canal-systems &c, of the 

 StromatoporcB are not normal productions, as we at present believe 

 them to be beyond any reasonable doubt, but " branching canals 

 bored by some low vegetable organism," as Moseley {I. c. p. 116) 

 avers is the case in Millepora and Pocillopora &c., and, further- 

 more, that other structural Stromatoporoid peculiarities are pre- 

 sent in undoubted members of the Hydrozoa, then we shall be 

 willing to admit their alliance with the latter, though certainly 

 they are aberrant types. With our present imperfect know- 

 ledge, and taking into account all the data for and against, we 

 must at present regard them as a group per se, or, as we think 

 justifiable on the positive and negative evidence, a new section 

 of the Calcareous Sponges, for which we propose the term Steo- 



MATOPOEOIDEA. 



DESCRIPTION OF THE PLATES. 

 Plate I. 



Fig. 1. Sfromatopora tuhcrculata, Nich. A small portion from the Corniferous 

 Limestone, Jarvis, Ontario, showing, above, the roughened nodular or 



