MINUTE STRUCTURE OP STROMATOPOHA AKD ITS ALLIES. 289 



each, or all together, forbid the idea o£ identity with Clatlirodlc- 

 tyon or its Stromatoporoiis allies. We have more especially di- 

 rected attention to the above families of Polyzoa as those posses- 

 sing the greatest likeness to the series of fossil forms at issue ; 

 for it is chiefly in the suborder Cheilostomata that the i^oly- 

 zoarium manifests skeletal likeness to most of the Stromato- 

 poroids. !N"evertlieless we would remark that among the sub- 

 order Cyclostomata the genera JIetero;pora^ De Blainville, and 

 Heteroporella, Busk*, possess more than a usual amount of 

 interest. Both have a surface furnished with openings of two 

 kinds, viz. cell-orifices and tubes, the latter penetrating the 

 polyzoarium vertically, and occasionally containing a kind of 

 imperfect sei:)ta. These structural peculiarities are sugges- 

 tive of Caunopora. Still they are deceptive resemblances ; for 

 in the Cyclostomata in question the canalicular cells or zooecia 

 run in close apposition alongside the tubular passages and in the 

 same vertical direction, whereas in Caunopora the thick-walled 

 tubes run diagonally to the laminse and sarcode-chambers, besides 

 others points of dissimilarity. In some species of Heteropora 

 Mr. Busk mentions the presence of a superficial stellate appear- 

 ance in connexion with the interstitial orifices ; but what relation 

 these may bear to the oblique radiating water-canals of the Stroma- 

 toporoids, we have not had the opportunity of accurately deter- 

 mining. It is sufficient for our purj)Ose to show that, besides 

 outward aspects, in other more important respects the diversity of 

 structure establishes distinction between the Cyclostomatous Poly- 

 zoa and Stromatopora. Turthermore, as a whole, in zooecia, ooecia, 

 vibracula, avicularia, tubules, porous walls, and a variety of other 

 minor particulars, the Polyzoa do not accord with any of the types 

 of the Stromatoporoids. 



Summary and Conclusion. 



In this communication we have first given an epitome of the 

 very diverse views held regarding Stromatopora up to the present 

 time. "We then treat of its fossil state, and show that, although 

 the remains have been preserved in several mineral conditions, 

 nevertheless the skeletal organization originally has been solely 

 of a calcareous nature. We further contribute data bearing on 

 the structural peculiarities, not only exteriorly and generally, but 

 as elucidated by microscopic research. It results that neither are 

 * * A Monograph of the Fossil Polyzoa of the Crag,' pp. 121 & 126. 



