244 Mr. J. Young on the Structure of 



structure originally existed or not. Other specimens, how- 

 ever, may yet prove this point one way or other. 



Messrs. "Nicholson and Foord state that the true cell-walls 

 of the autopores do not surround the whole of the tube in its 

 dense or opaque condition, but blend at the point where the 

 folds occur into the layer of lighter crystalline calcite that 

 forms the raised lips of the cells, stating (p. 498) that " it will 

 be noticed that the fold is of a lighter colour than the other 

 part of the cell-wall." This does not appear to be a cha- 

 racter of any value, as I find in my best-preserved sections that 

 the true cell-wall is often quite persistent in its density and 

 darker colour around the tubes, even where they are thickened 

 at the folds by the layer of sclerenchyma. In my sections it 

 is sometimes seen that the walls of certain cells do blend and 

 disappear in some instances where they are covered by the 

 lighter calcite layer ; but these same sections also show in 

 other instances the walls quite complete around the majority 

 of the cells, and this complete condition of the walls is seen 

 to exist in nearly all the sections in which the tubes have 

 become erect and the mouths of the autopores more circular. 

 The disappearance of the cell-wall around the folds in those 

 instances where it is seen to be wanting seems to be due to 

 some kind of absorption of the denser calcite and its replace- 

 ment by the sclerenchyma either when the organisms were 

 living or afterwards by some process or other during fossiliza- 

 tion. It, however, is seen to be a variable character even in 

 the same specimen. 



Having stated this much regarding the structures I for- 

 merly found in F. incrustans I will here further notice shortly 

 one other interesting structure that I have recently dis- 

 covered in specimens obtained from Bowiield, Renfrewshire, 

 near Glasgow. The form of Fistulipora found at this place 

 may yet prove to be a distinct species from, or variety 

 of, F. incrustans; but beyond the difference in the form of 

 its zoaiium and the structure to be noticed there seems to be 

 little difference either in the form of the autopores or in the 

 number and arrangement of the mesopores and macuUe from 

 those seen in the older stages of some specimens of F. itia^us- 

 tans. The organism is generally found in the form of frag- 

 ments of branching, subcylindrical, hollow stems, varying in 

 thickness from one quarter to half an inch in diameter, the 

 interior of the stems being now filled by a deposit of clay- 

 ironstone. The new internal structure that I have to note in 

 this species consists of a group of slender spines that are seen 

 in the sections to radiate from the inner wall of the autopores 

 to near the centre of the tubes. These radiating spines have 



