AND PELAGIC SURFACE-SWIMMING SPECIES. 303 



cavity in C. bathymetricus does not terminate, as in C. membranaceus, above the line of 

 commencement of the mesenteries, but is continued downwards for some distance, its 

 walls consisting of a thin and delicate membrane, supported by the mesenteries and 

 having an irregular lower border. This lower sac is evidently in this case the true 

 stomach, since it was filled in the specimen examined with food, consisting of Globigerina- 

 shells together with small Crustacea. The main part of the mesenteries are not con- 

 tinued to the apex of the body, but only extend down about 3 millims., and from these 

 mesenteries are prolonged the ovaries, beyond the terminations of which is a clear space 

 of about 7 millims. in length. There is no canal formed of the opposed mesenteries and 

 leading from the mouth to the posterior part of the body-cavity ; but this is represented by 

 three or four stout muscular threads derived from the mesenteries, which are attached 

 to the inner surface of the body-wall near the posterior opening. These muscular 

 threads are branched superiorly, and thus each is derived from two or more mesenteries. 

 The animal was not examined until it had been put with its tube in spirit, under the 

 belief that it was an annelid, and its colouring, if it had any, was therefore destroyed. 

 Only two kinds of nematocysts were found in it, although portions of the epidermis, 

 the tentacles, and the test were examined. 



The large, characteristic Cerianthus thread-cells, which form the main bulk of the 

 animal's tube, resemble those of C. membranaceus in all respects except that the thread 

 is wound in an even spiral around the periphery of the internal cavity of the cell, the 

 axis of the spiral being at right angles to the longer diameter of the cell. In C. mem- 

 branaceus the thread is, as figured in Bronn (I. c. Taf. 1. fig. 7), irregularly doubled up 

 inside the cell. These cells are in G. bathymetricus "06 milling, long by "03 millim. broad. 



The other kind of thread-cell observed was of the common elongated ovoidal form, 

 with the thread wound in a spiral about the longer axis of the cell (fig. 5). The 

 largest of these cells are of the same length as those forming the bulk of the test, but 

 they are very much more slender. They are not very abundant in the test, but occur 

 in large numbers on the tentacles. Thread-cells of all sizes and stages of development 

 are to be found in various regions of the body but all of them are referable to these two 

 forms. 



C. bathymetricus differs from the hitherto described species in the number of tentacles 

 arrangement of the digestive cavity, absence of a canal formed by the mesenteries, 

 the form of the thread- cells, and in its very small size. Two specimens were obtained 

 on June 19th 1873, in 2750 fathoms, in lat. 35° 29' N., long. 50° 53' W., between the 

 Bermudas and the Azores. 



General Remarks. 



The occurrence in the deep sea of representatives of well-known shallow-water forms 

 of Actiniaria is of considerable interest. The Edtvardsia here described seems to have 

 undergone no modification of any moment in a descent to 800 fathoms. The Ceri- 

 anthus, which is from the great depth of 2750 fathoms, is much dwarfed, and differs 

 in some details of its anatomy from the shallow-water forms; but it is astonishing 

 that the same genus should be able to adapt itself to shallow tropical seas and the ice- 



SECOND SERIES. — ZOOLOGY, VOL. I. 2 S 



