A MONOGRAPH 



BEITISH STKOMATOPOROIDS 



I. HISTORICAL INTRODUCTION. 



The singular extinct organisms of which the genus Stromatojjora, Goldfuss, is 

 the central type, and which we may conveniently speak of by the general name of 

 the " Stromatoporoids," constitute a great group of fossil Invertebrates, which 

 are specially characteristic of the Ordovician, Silurian, and Devonian formations, if 

 not absolutely confined to strata belonging to these periods. Possessing a calca- 

 reous skeleton, and often attaining to very considerable dimensions, they enter 

 very extensively into the formation of many of the older Palaeozoic limestones. 

 Abundant as they are in the Silurian and Devonian deposits of various regions, 

 the investigation of their structure is attended with peculiar difficulties ; and it is 

 not therefore surprising to find that the most diverse views have been entertained 

 as to their nature and zoological relationships. The groups to one or other of 

 which they have been most commonly referred are the Sponges, the Foraminifera, 

 the Corals, and the Hydrozoa. The results, however, of the most recent investi- 

 gations, render it hardly a matter of doubt that they are truly referable to the 

 Hydrozoa, and that they are more or less closely related to the Hydrocorallines on 

 the one hand, and to the Hydractiniidce on the other. The general progress 

 of scientific research as regards the Stromatoporoids will, however, be best 

 gathered from the following brief historical summary : 



The genus Stromatopora was originally founded by Goldfuss (' Petrefacta 

 Germanias,' Bd. i, p. 21, 1826), and was defined by him as including hemispherical 

 Corals, with a calcareous skeleton composed of alternating dense and porous layers. 

 He originally assigned to the genus a place between the Millepores and the Madre- 

 pores, but in a later portion of his great work he expressed the opinion that the 



