NATURAL HISTORY SOCIETY OF GLASGOW. 27 



With the view of comparing sections of stems possessing aper- 

 tures and passages with those in which the branch canals leading 

 to the auxiliary side-arms, and the mode of articulation of the arms 

 themselves are exhibited, I have given two sections, one of them 

 horizontal, and the other vertical (PI. I. figs. 20 — 21). The marked 

 difference between the articular sockets in these and the pocket-like 

 apertures in PI. I. figs. 10, 11, 12, and 13 is at once apparent. 

 There is a nearer approach to them in the aperture and passage 

 seen in PI. I. figs. 5 and 7, but I do not think it is sufficiently strong 

 to warrant us in concluding that these holes on the exterior of 

 Crinoidal columns, and the passages leading from them, are merely 

 the enlarged sockets of the auxiliary side-arms and the branch 

 canals connecting them with the large columnar canal. 



The examination of a large number of injured and enlarged 

 Crinoid stems, and sections made from them, lias led me to the 

 conclusion that they may be provisionally placed under one of 

 three heads, viz.: — 



1. Those in which there is no trace of aperture or canal, but 

 simply an enlargement of the column — the cause of the latter 

 being sometimes present and apparent, at others not. 



2. Those in which the aperture is usually round, or oval, leading 

 into a short pocket-like cavity, and not communicating with the 

 central canal. 



3. Those in which the aperture is more or less irregular, leading 

 into a similar passage placed in connection with the columnar canal. 



4. Agents and Influences which Produce the Enlargement 



of Crinoidal Columns. 



There can be no possible doubt that, in a large number of cases, 

 enlargement is produced originally by the external attachment 

 of bodies to the stems, foreign to the life and well-being of the 

 particular individual attacked. Of this nature there may be 

 enumerated — 



1. Cladochonus crassus (M'Coy). — This coral has been satis- 

 factorily shown by the late Mr. Rofe to attach itself to the stems 

 of Crinoid s, and to produce in them some very extraordinary 

 examples of distortion. I have had an opportunity of examining 

 Mr. Rofe's types, now in the British Museum, and can bear testi- 

 mony to the accuracy of his descriptions in the Geological 



