American Palaeozoic Bryozoa. 



135 



former, is unusually and normally free; but it is very difficult to 

 explain this fact, if there be any developmental relationship between 

 the two. Thirdly, as regards matters of actual observation, I have 

 never been able to detect anything of the nature of a "Cerampora 

 stage" in young Monticuliporce. This is a point which is most easily 

 observed in young examples of the discoidal species of Monticulipora, 

 such as M. petropolitana and the various forms allied to this; and I 

 can only say that the most minute examples of these forms which have 

 come under my notice, differ in no respect whatever, that I can detect, 

 except size, as regards their external and internal characters, from 

 fully grown specimens. Fourthly, if it were the case that discoidal 

 species of Monticulipora, such as M. petropolitana, Pand., grew out 

 of the thin parasitic crusts to which Hall applied the name of Ceram- 

 opora, we ought to be able to detect the primitive " Ceramoporoid" 

 portion of the colon}^ at the base of thin vertical sections of colonies 

 of the former. I have, however, examined a large number of such 

 sections, and I have been unable to detect any difference in the 

 structure of the lowest portion of the tubes, restiug directly upon the 

 basal epitheca, as compared with that of the full grown portion of the 

 corallites. Dr. Lindstrom states that the basal surface of a Monticu- 

 lipora, when its epitheca is veiy thin, "clearly shows that it is a 

 Ceramopora," but I am unable to concur in this statement. If the 

 specimen be undoubtedly one of Monticulipora, then I have never 

 seen anything in its epithecal surface which could be compared with the 

 structure of Ceramopora." My own views upon the subject are, 

 probably, in some points, intermediate between those of the authors 

 quoted. I agree with Dr. Nicholson in rejecting the theory that 

 Monticulipora was developed from a Ceramopora ; but I believe him 

 to be in error when he makes the statement that there is no difference 

 between the lowest portion of the tubes, as compared with that portion 

 some distance above the epitheca. In the massive, incrusting and 

 double-leaved species of Monticulipora, that portion of the tubes 

 resting directly upon the basal membrane, is prostrate, remaining so a 

 short time, when they bend abruptly upward, attaining an erect posi- 

 tion and the characters of a fully developed tube. This character 

 gives to specimens with a thin epitheca a peculiar appearance, which 

 is especially well shown in the incrusting species. At Cincinnati, col- 

 lectors frequent^ obtain specimens which had grown upon the inside 

 of the body chamber of some cephalopod or bivalve shell. The shells 

 of thuse mollusks having been destroyed during the process of fossil- 



