Lindstrom — On Zoantharia Rugosa. 359 



to the smallest wall, on whicli it continiies, so tliat the median 

 septum of that wall is enclosed by it. It is exactly the same groove 

 or pit which may be observed in Cyathaxonia, and so highly 

 characterizes the Zaplirentlncs, in several of which it surrounds the 

 large primary septum. It also occurs in the genera Ompliyma, 

 Calceola, Gijstiphyllum, Bhizophijllum, and Cyathopliyllum. It is always 

 situated in the same line as the two largest primary septa, on the 

 longest and convex side in the Zaphrentincs, and on the shortest 

 in the Cyatlwphyllina. This groove is not to be confounded with the 

 rarer and more shallow depressions of a cruciform arrangement 

 in the Ompliymce (the "fosses septales " of Milne-Edwards). 



The principal mass of the solid interior of the shell consists of 

 vesicular basin-shaped layers (Plate XIY. Fig. 5) approaching the 

 structure of Omphyma, Very small specimens are sometimes fixed 

 with their rootlets on the uppermost edge of the calyx, and project 

 from the interior walls of the parent. This phenomenon corresponds 

 to what is seen in the genera Cyatliopliylluin, Acervularia, and others, 

 and is no doubt to be regarded as a kind of budding. Goniophyllum 

 pyramidale also shows signs of these interruptions in the continuity 

 of the growth, so peculiar amongst the Bugosa. The animal some- 

 times diminished its compass, and commenced to form a new calyx 

 within the old one. This new calyx is either completely furnished 

 with new walls, or it is in part formed of the old ones (Plate XIV. 

 Figs. 4 and 12). 



The smallest examples very much resemble Calceolce in their pro- 

 minent primary septum (Plate XIV., Fig. 3). But the form of the 

 mouth soon becomes triangular, and at a length of ten millims 

 trapezoidal. In some specimens the shell preserves a three-sided 

 pyramidal form, the full-grown animal retaining the same shape as 

 when young. Instances of this, however, are not wanting in the 

 living creation, as in some fishes, Crustacea, and mollusca. ^ 



The operculum of this fossil, found fixed in its place, as well as 

 in many instances detached, is generally of a regular trapezoidal 

 shape (Plate XIV., Figs. 6 and 7), but it is also triangular. It is 

 attached at its broadest margin (here called the cardinal margin) 

 at the uppermost border of the calyx. Its exterior surface is 

 quite smooth, with the exception of the lines of growth (Plate 

 XIV. Fig. 6). The nucleus is above the centre, near to the 

 cardinal line. The middle of the outer surface is depressed in a 

 sinus, extending from the nucleus to the shortest margin, and of the 

 same breadth. The innermost layers being thus the most depressed 

 of all, no surface resembling an " area " is formed at the cardinal 

 margin, only a very narrow rim. On the interior siurface of the 

 operculum (Plate XIV. Fig. 7) there is, close to the cardinal-margin, 

 a narrow sloj)ing area, which is joined in an obtuse angle with the 

 other surface. This again is divided by a median tooth or ridge into 

 two similar parts, sloping towards the side-margins. The median 

 ridge is highest on the point where the cardinal area meets the other 



^ This Prof. S. Loven has found to be the case in Cottiis qiuzdricornis, Idotea ento- 

 mon, etc., and I have myself ascertained the fact in Paludinella baltica, Nilsson. 



