REPORT ON THE ACTINIARIA. 49 



same pair are never of the same size, so that for example half of the septa of the fifth cycle 

 are inserted at a considerable distance on the oral disk, whilst the other half run only to 

 two-thirds of the height of the wall. Closer investigation shows that this difference of 

 size is governed by fixed laws. From the moment when the septa of the first two cycles are 

 developed onwards, we find that after these all the interseptal spaces are bounded by septa 

 of different grades, i.e., by a septum of a higher and a septum of a lower order. The pro- 

 pinquity of the former causes a stronger development, e.g., in the newly-formed pairs of the 

 third order, the septum turned towards the older pair is always stronger than the other. 

 In the following pair of the fourth order, the septum which adjoins the septum of the 

 third order is always the smaller. These differences cannot, of course, arise in the second 

 cycle, as the interseptal space lies between septa of the first order which are of equal value. 

 As Dysactis crassicornis is not found at any great depth, and was dredged up by the 

 Challenger at several places, the probability that the animal may have come under the 

 observation of former naturalists deserves special consideration. Let me draw attention 

 to two forms which are perhaps identical with it. In the Annals and Magazine of 

 Natural History, 1872 (series iv., vol. ix. p. 304), Kyle describes an Actinia which he 

 procured by means of the hooks on fishermen's deep-sea lines. Like the form under 

 discussion, this Actinia reminds us of Tealia crassicornis, but differs from it in having a 

 smooth body surface which brings it nearer our Dysactis. The second Actinia is the Rho- 

 dactinia davisii, minutely described by Verrill (Mem. Boston Soc, vol. i. p. 18, 1866-69), 

 in which the papillae on the wall are so indistinct that the surface appears almost smooth. 

 The tentacles also appear to be similar, and, according to Verrill, are numerous, and 

 arranged in several indistinct rows ; they are conical or cylindrical, thick, rather short, 

 rounded obtusely at the end or even club-shaped. There is, however, some doubt about 

 this second form, as Verrill himself identifies it with Tealia crassicornis or rather Urticina 

 crassicornis, as he terms the species (Transactions Connecticut Acad., vol. i. p. 469). 



Dysactis rhodora. 



Actinia rhodora, Couthouy, in Dana, 1 Explor. Exped., Zoopli., p. 118, pi. iv. fig. 37, 1846 



(Synopsis, p. 11). 

 Dysactis rhodora, Milne-Edwards, Hist. des. Corall., torn. i. p. 2G3, 1857. 



Tentacles tolerably long and slender, arranged in three rows ; the tentacles of the 

 inner row essentially longer and stronger than those of the middle and outer rows. 



Habitat— Station 313. January 20, 1876. Lat. 52° 20' S., long. 68° 0' W. Depth 

 55 fathoms. Two strongly-contracted specimens. 



1 The edition of Dana's chief work, Report on the Zoophytes of the U.S. Exploring Expedition, which appeared 

 in 1846, was very limited, and was soon out of print ; the author therefore subsequently (1859) published a 

 synopsis. I was only able to refer to the synopsis and the atlas, for the loan of which I am indebted to the kindness 

 of Prof. Ha;ckel. The quotations referring to the large work are taken from Milne-Edward's Histoire des Coralliaires 

 whilst I have myself looked over the synopsis and the atlas. 



All the quotations have been verified in the Challenger Office by reference to the original work. — J. M. 



(ZOOL. CHALL. EXP. — PART XV. — 1882.) p 7 



