412 Lindstrom — On Zoantharia Rugosa. 



originate at the straigMest margin. This must be considered as the 

 cardinal margin and the others, where the striae end as the lateral 

 margin. Next within this border there is a depression with small 

 pits between the stri^. This operculum belongs to a type quite 

 different from that of the preceding fossils, being destitute of any 

 prominent ridge in the middle, but it may, as I suppose, have been 

 fixed to an animal of the same class. Its shape as well as its inte- 

 rior surface make it im2D0Ssible to join it with any of the Gasteropoda 

 which occur in the same stratum, and which are all Holostomata. 

 Nor is there any tube of Annelids to which it might have belonged. 

 The strije on the inner surface are, in all probability^ homologous 

 with those of Goniophyllum situated on both sides of the median 

 ridge. In the same stratum with this operculum there occurs only 

 a species of Hallia, to which it in some degree corresponds. It has 

 not yet been decided with certainty if there is a true connection 

 between both, as the outlines of the caljx and the operculum are 

 somewhat dissimilar. The area on the interior surface of the oper- 

 culum within the border has, nevertheless, the same semicircular 

 form at the mouth of the calyx, so that it is highly probable that 

 they were connected and that the elevated border of the operculum 

 projected outside the rim of the calyx when this was covered by the 

 operculum. The shell of this Hallia, which, by reason of its exterior 

 resemblance to Calceola, may be named Hallia calceoloides (Plate 

 XIV. Figs. 19-21), has one surface flat and the other convex, the 

 former, with a middle ridge consisting of two or three folds. 

 Towards this ridge other smaller folds converge in a pinnate arrange- 

 ment. When the shell has attained a length of about 25 millims its 

 flat surface also becomes convex, and the form of the shell is cylin- 

 drical. On old specimens the outline of the calyx is circular, in 

 younger ones semicircular. The shell is long and slender, sharply 

 pointed, without any rootlets. In the interior of the calyx (Plate 

 XIV. fig. 21) there is only one large septum of the first order, so 

 characteristic of the genus Hallia. It is sitiiated on the middle of 

 the flat wall and reaches to the bottom of the calyx. It is sur- 

 mounted on both sides by septa of a second order, which correspond 

 with one another. They are 28 in number, with smaller ones 

 between them, which only extend half as far as the wall. The septa 

 continue, uninterrupted by tabulse, &c., to the middle axis of the 

 shell. 



Many more specimens of Z. rugosa than those now mentioned 

 have been provided with an ojoerculum. The description and the 

 figures of Guettard of a Cyathophyllum^ with an operculum are suf- 

 ficiently clear and evident not to be doubted any longer. It has 

 already been mentioned that Professor Steenstrup observed a Cyaiho- 

 pJiyllum mitratmn with a fragment of the operculum still in situ. He 

 has also remarked that a small border noticeable around the interior 

 rim of the calyx indicates, in many species, that they probably had 

 an operculiun. 



I have been favoured with a kind communication from Thomas 

 1 Memoires, yoI. iii., p. 510, plate 52. 



