THE NATURE OF CAUNOPORA. 117 



poroids " Caunopora-tubes " wero associated, it was a not unreasonable conclusion 

 that the forms possessing these singular structures were really distinct genera. 

 Bargatzky was the first observer who directed his attention specially to the minute 

 structure of the tissue enveloping the tubes ; and he showed, quite rightly, that 

 this tissue is sometimes of the completely reticulated type, while at other times the 

 reticulation is incomplete. On this difference — which is really the difference 

 between Stromatopora, Goldf., and Stromatoporella, Nich. — he based his separation 

 of Diapora, Barg., from Caunopora, Phill. As already pointed out, it would 

 appear that there are only certain particular types of the Stromatoporoids which 

 habitually form " Caunoporoid " colonies, and that other common and well-known 

 types rarely or never do so. For example, the species of Actino stroma, which 

 occur in such vast numbers in the Devonian Rocks of Britain and Germany, seem 

 hardly ever to form " Caunopora}." They very commonly envelop Corals of different 

 kinds in the course of their growth ; but with the exception of a single specimen 

 in the collection of Mr. Champernowne, I have never met with an example of the 

 genus associated with the regular " Caunopora-tubes." No Labechia has ever been 

 recorded as giving rise to " Caunopora" colonies, though the coenosteum in this genus 

 also quite commonly grows round and envelops Corals or other foreign organisms. 

 Similarly, the species of Glathrodictyon are almost never observed with associated 

 " Caunopora-tubes." With very few exceptions, all the " Caunopora}" and "Diapora?" 

 which I have examined belong, as regards the investing Stromatoporoid, to the 

 family of the Stromatoporidm, and to one or other of the two genera Stromatopora, 

 Goldf., and Stromatoporella, Nich. Moreover, all the species of these two genera 

 which are of common occurrence as " Caunopora}" and " Diapora}," occur also without 

 the embedded tubes, the two " states " of each species being often found side by side 

 in the same locality. The species of Stromatopora and Stromatoporella which are 

 most commonly concerned in the production, respectively, of " Caunopora} " and 

 " Diapora} " are the following : 



(a) Stromatopora concentrica, Goldf. (Plate XI, figs. 16 and 17, respectively 

 with and without " Caunopora-tubes "). 



(b) Stromatopora Hupschii, Barg., sp. (Plate X, figs. 8 — 12, with the "Cauno- 

 pora-tubes ;" woodcut, Fig. 6, without the tubes). 



(c) Stromatopora bucheliensis, Barg., sp. (Plate X, figs. 6 and 7, with the 

 " Caunopora-tubes;" woodcut, Fig. 6, without the tubes). 



(d) Stromatopora Beuthii, Barg., sp. 



(e) Stromatoporella laminata, Barg., sp. (Plate X, figs. 1 — 4). 

 (/) Stromatoporella eifeliensis, Nich. 



The species of Stromatoporella have not yet been worked out, and I do not know 

 whether there are any species of this genus which never form " Diapora " colonies. 

 I have not, however, so far, found the type-species of this genus, viz. S. granulata } 



16 



