124 BRITISH STROMATOPOROIDS. 



but form thin, laminar expansions, often of great size, the thickness of which varies 

 from 4 — 6 mm. up to perhaps 2 — 4 cm. In such cases, the embedded tubes, if set 

 free from their investment, would be quite unlike any known Syringopora, and 

 would much more closely approach the general characters of an Aulopora-colonj. 

 In the second place, there are no known species of Syringopora which possess such 

 exceedingly delicate tubes as those of many " Gaunopora" and " Diaporce." In 

 many examples of the latter I find the tubes to be not more than perhaps ^ mm. 

 in diameter, and they are sometimes even smaller than this (Plate XI, fig. 17). 

 As regards the Devonian species of Syringopora, Schliiter (' Sitzungsberichte der 

 niederrhein. Gesell.,' 1885) states that his S. tenuis has the smallest tubes of any 

 species of Syringopora known to occur in the Middle Devonian of the Rhenish 

 region, in which " Caunoporce " are very abundant. The diameter of the corallites 

 in this species are stated not to exceed 1 mm. ; and in the Syringopora moravica of 

 Ferd. Roemer (' Leth. Pal.,' p. 495), from the Devonian of Olmiitz, the corallites are 

 said to be only § mm. in diameter. In both of these, however, the diameter of the 

 corallites much exceeds that of the tubes of many " Caunoporai," and the tubes in 

 most species of Syringopora are much larger than in these two. 



In the third place, the massive examples of " Gaunopora" which otherwise 

 most resemble Syringopora;, have the tubes much more regularly spaced, and much 

 more uniformly parallel, than we see them to be in any known species of the genus 

 Syringopora. In many specimens in which the entire colony may be some inches 

 in thickness, the mass is traversed throughout by straight parallel tubes which 

 may be from ^ to ^ mm. in diameter, and which on an average are placed at about 

 a millimetre apart. On the other hand, in all the known Syringoporai the tubes 

 are not only thicker, but much more irregular in their growth, being invariably 

 more or less flexuous, and thus more or less intertwined with one another. 



Again, we have not at present any right to assume that septal spines are always 

 present in the tubes of " Gaunopora." The discovery of these structures in certain 

 " Caunoporai" and " Diaporce" has certainly greatly lessened the difficulty 

 of accepting Syringopora as the " commensal " of these fossils, but many 

 excellently preserved specimens show no traces of these structures, and they do 

 not seem therefore to have been uniformly present. On the other hand, all the 

 Syringoporai appear to possess septal spines in the corallites. 



Lastly, there are formations or localities in which " Caunoporos " and " Diaporos " 

 are very abundant, but in which no examples of Syringopora have ever been 

 detected. Thus at Biichel in the Paffrath district, we find an enormous number 

 of " Caunoporai " and " Diaporm" but no single example of a Syringopora has 

 ever been found, though Aulopora-colonies are sufficiently abundant. This is true 

 also, so far as I am aware, of another well-known German locality, viz. Gerolstein 

 in the Eifel. It is also true, in a general way at any rate, of the Devonian Lime- 



