NATURAL HISTORY SOCIETY OF GLASGOW. 25 



no trace whatever of an opening could be detected. The specimens 

 were small and could not be cut without destruction. Similar 

 specimens are noticed by the before-mentioned authority. 



The column at or about the aperture is usually flattened or 

 impressed, or it may become quite concave. The opening is some- 

 times large and distinctly visible, at other times only represented 

 by a mere dot (PL I. tigs. 1-4 and 15); and again examples are before 

 me in which its former existence is only indicated by a general 

 depression of the surface. When well marked, the openings are 

 either oval, oblong, round, irregular in form, or may possess a 

 pinched appearance. The margins are usually rounded and directed 

 inwards, but one case is described by a " Corresponding Member," 

 where the hole had everted edges.* A good example of a small 

 round, or circular, hole is shown in PL I. fig. 14, or fig. 15. The 

 irregular form is seen in PL I. fig. 1, where the depression in which 

 it occurs is much elongated vertically ; or again in PL I. fig. 16, where 

 the aperture is transversely elongated and much puckered at the 

 corners, and with a gradual closing over of the substance of the 

 stem. The holes arising from this irregular condition are also 

 exhibited in a marked degree by those stems attacked by Productus 

 coniplectens (mihi), PL II. figs. 2, 3, and 4. 



As to the internal structure of these swollen stems, with the 

 view of demonstrating this I have had prepared a number of cross 

 sections of various stems, by means of which we shall be enabled 

 to gain an insight, of a more or less complete nature, into the 

 ultimate course and probable use of the apertures in question, and 

 of the passages into which they lead. 



It will be observed that in some sections (PL I. figs. 10 — 13) the 

 holes lead into mere pockets, as it were, in the substance of the 

 columns, and do not by any means reach the central canal. The 

 pocket is itself frequently filled with a plug of calcareous matter 

 (PL I. figs. 10, 11, and 12), but usually separated from the wall 

 of the cavity by a thin, dark lining of matrix. This peculiar 

 pocket-like opening Las much the appearance of an inversion of 

 the stem-wall, arising probably from its external rounded edges 

 (PL I. fig. 13), which, in some instances at least, are produced by 

 the subsequent growth of the stem to repair the injury done. 



In other sections the apertures will be seen to lead directly into 



* Loc. cit., p. 94. 



