8 Scientific Proceedings, Royal Dublin Society. 



mination. Similar pores, which by the way are very difficult to 

 observe, were found in Ealcampa clams, Quoy and Gaim, by E. 

 Hertwig, and I have also seen them in the so-called Halcampa 

 fultoni, St. Wright. These perforations enable the physa to be 

 suddenly emptied of its contained water. They exist in large 

 numbers in Peachia hastata, both Mr. Dixon and myself being 

 now satisfied that such is the true explanation of the appearances 

 we described (/. <?., p. 403). The whole body is continually under- 

 going slow waves of alternate contraction and expansion. As 

 Gosse states, the body is capable of great extension (" extending 

 to ten times its diameter or more). . . Specimens reach to an inch 

 and three-quarters in length, and one-eighth of an inch in average 

 diameter; the extremity is frequently inflated to one-fourth." 



My longest specimen was about 50 mm. (2 inches) in length, 

 and about 3 '5 mm. (-3% of an inch) in diameter at the middle. 

 Other specimens measured about 31 mm., 38 mm., 44 mm., &c. 

 (1± in., 1| in., If in.) in length. 



In nearly every case the tentacles, although monocyclic and 

 perfectly uniform in size and shape, appeared to consist of two 

 series. Those of the first series, which for the sake of conveni- 

 ence I term the primaries, are usually carried more or less arched 

 forwards and inwards, and are also almost invariably more pro- 



with the octoradial Edwardsise ? " [In connexion with, the last paragraph I would 

 quote the following from Dr. R. Hertwig' s Report on the Actiniaria, Challenger Re- 

 ports, Zoology, vi., 1885, p. 95.]: — 



" The constitution of the septa in Halcampa cavus [Quoy et Gaim] shows further 

 peculiarities worthy of notice, which seem to me to indicate its relation to the Edwardsiae. 

 As I was preparing a series of sections through one-half of the physa of the larger spe- 

 cimen, it struck me that three septa [mesenteries] (including the pair of directive septa 

 [mesenteries]) were not so strong as the other septa, inasmuch as their longitudinal 

 muscular cords became sooner indistinct (pi. xiii., fig. 7.) In the second smaller Hal- 

 campa, in which I was able to make sections through the entire body, four septa were 

 somewhat smaller than the eight others ; and, finally, Strethill Wright has described a 

 parasitic Halcampa living on Medusse (Halcampa fultoni), in which he can distinguish 

 four stronger and eight weaker septa (Ann. and Mag. Nat. Hist., ser. in., vol. viii., 

 p. 133, 1861). All this shows that an unequal development of the septa, and, consequently, 

 a difference in their morphological value, is not unusual in Halcampa. If we assume 

 that the eight stronger septa are homologous with the septa of Edwardsia, whilst the 

 four other septa are new formations, then the genus Halcampa would present us with 

 transition forms between the Edwardsiae and the Hexactinise." [As the present com- 

 munication is merely a critical note on the identity of the species in question, I do not 

 intend on this occasion to follow up the line of thought here suggested. — A. C. H.j 



