24 PROCEEDINGS OF THE 



method adopted by certain corals and polyzoa, of attaching them- 

 selves to living and dead Crinoid stems. In one case where a 

 colony of Chaetetes tumidus had attached itself, the growth of the 

 stem was apparently hindered and interrupted ; for the stem beyond 

 the edges of the cluster is enlarged, whereby the former is raised 

 above the general level of the periphery, and enveloping, as it were, 

 the coral. I give an exceedingly good figure of a similar occurrence 

 (PI. I. fig. 17, PI. II. fig. 7), and shall return to the subject further 

 on. A " Corresponding Member" also shows how the hole usually 

 seen on these injured Crinoids is in one instance occupied by the 

 root and part of the stem of a polyzoon. 



3. — Description of Specimens. 



As a rule we find the enlargement of Crinoidal columns, now 

 under discussion, to consist of a gradual expansion of the stem at 

 some definite point in its course. Generally the enlargement is 

 gradual (PL I. figs. 1, 4, 6), the stem returning above the swelling 

 to much the same diameter and shape as at the point below where 

 the irregularity first manifested itself. Irregular and contorted 

 enlargements are, however, met with (PI. I. fig. 8); but cases of 

 sudden expansion, so far as my own observation has gone, are rare. 

 The chief modification appears to be, that one of the sides of the 

 enlargement becomes flattened, and more or less concave (PI. I. figs. 

 1 and 8), or, as pointed out by a "Corresponding Member," both may 

 become so.* Of the former modification good examples are seen in 

 the figures of Ure and Miller. Externally the separate segments or 

 " ossicles " of the column undergo little or no change (except in one 

 variety of swelling, to be more particularly referred to hereafter) 

 beyond that necessary to assist in the general formation of the en- 

 largement and some slight alteration in the surface ornamentation, 

 as described by a " Corresponding Member." The same authority 

 also noticed that a thickening of each ossicle took place, resulting in 

 an elongation of the stem generally. 



In very few cases which were not attributable to the loss of a 

 side-arm have I met with a swelling or enlargement unaccompanied 

 by an aperture or puncture, or the remains of one, at some point 

 in the enlarged periphery. The best marked of these proved, on a 

 section being made, to arise from such a course, but in the others 



* Proc. Nat. Hint. Soc. Glasgow, 1876, III., pt. 1, p, 94. 



