30 PROCEEDINGS OF THE 



Favosites between two enlargements of Crinoidal matter — an upper 

 and a lower (PI. II. fig. 7). Round the edges of the coral can be 

 seen a gradual closing-in of the substance of the stem, similar to 

 that seen in PL I. figs. 16 and 17. 



3. The Stems of other Crinoids. — The diligent collecting of Mr. 

 James Bennie, of the Geological Survey of Scotland, has brought 

 to light a number of intertwined and tangled stems from the Car- 

 boniferous limestone series of Dunbar. By means of these small 

 specimens we are made acquainted with the fact that attachment 

 of one Crinoid stem with the other took place in a most complete 

 manner. By what means, and from what cause union first took 

 place we are unable to say, but this having been effected, one, and 

 sometimes both individuals, set to work to absorb or envelope 

 one another, by the deposition of matter round about and over its 

 offending neighbour, until the one had wholly enclosed that portion 

 of the other lying across its stem, had only partially done so at the 

 expense of considerably enlarging itself, or had finally formed, with 

 the aid of others, an irregular and confused mass of Crinoid stems. 



Polyzoa. — A "Corresponding Member" has already pointed out 

 the manner in which Polyzoa and their roots become attached to 

 Crinoid stems. By the aid of an exceedingly instructive specimen, 

 from Roscobie, obtained by Mr. James Bennie, and now in the 

 Collection of the Geological Survey of Scotland, I am in a position 

 to show how even these delicate organisms can be the cause of 

 enlargement in Crinoidal columns. In PI. I. fig. 16 the usual 

 polyzoal incrustration, which in this particular case appears to 

 be a species of Archaeopova, has been gradually overlapped at its 

 edges by the substances of the stem, and encroachment has taken 

 place for some distance. The expanse occupied by the network 

 must have been of some size, judging by the dimensions of the 

 present depression in the stem. The manner in which the enclosure 

 has taken place, with the obtusely rounded edges of the overlapping 

 Crinoidal substance, is quite perceptible, together with the grooving 

 or puckering left by its advance. 



Produclus complectens (milii). As one of the causes of enlargement 

 of Crinoid stems, we must take into consideration the action of the 

 peculiar little brachiopod I described some time ago under the 

 above name* A large number of small Crinoid stems were met 



•& v 



*t« 



On an adherent Productus," &c, Quart. Jour. Oeol. Soc, 1875, 



