S6 



Genus IV. Alcyonella, LamarcK; 1816. 



Name. — A diminutive noun, formed from Alcyonium, a genus of marine Actninozoal 

 Radiata. 



The animal originally described by Pallas, under the name of Tuhiilaria fungosn, and 

 by Bruguiere under that of Alcyonium Jluviatile, was assumed by Lamarck as the type of a 

 new genus which he named Alcyonella ; but, deriving its characters from the very incorrect 

 description and figures of Bruguiere, Lamarck's definition of the genus is necessarily 

 erroneous, 



Some naturalists insist on the identity of the genera Alcyonella and Plumatella, and go 

 so far as to maintain that the animal described under different names, by Pallas, Bruguiere, 

 and Lamarck, possesses no essential character to distinguish it even specifically from P. repens 

 or P. campannlata, the difference being solely the result of accidental causes — especially the 

 form and size of the object to which it is attached — operating on it during its growth, and thus 

 influencing its development. The author who has most elaborately defended this view is 

 M. Raspail, and a similar opinion has been advocated by Ehrenberg and Siebold. After, 

 however, much attention to the subject, 1 have satisfied myself that there are sufficient 

 grounds for keeping the two groups generically distinct. It is quite true that, in its young 

 state, Alcyonella has its tubes distinct, creeping along the surface of the supporting body, and 

 in this condition, I admit that it cannot be distinguished from a Plumatella, but it is only in 

 its early youth that it presents this form. Plumatella, on the other hand, preserves a dis- 

 tinctness of its tubes throughout its whole existence. I have found very large specimens of 

 Plumatella under precisely the same circumstances as those in which we meet Alcyonella, and 

 yet without the slightest tendency to assume the form of the latter genus. Another argument, 

 which strongly supports the view here taken, is derived fi'om the fact that Alcyonella has not 

 yet been detected in Ireland,* though Plumatella rejyens is exceedingly abundant throughout 

 the island, frequently presenting the utmost luxuriance, and yet invariably preserving a total 

 distinctness of its tubes, no matter what the form or size of the object on which it grows. 



In distinguishing the species of Alcyonella, 1 have employed characters drawn chiefly 

 from the general habit of the animal, the structure of the coenoecium, and the shape of the 

 statoblasts. We have seen, in the anatomical section of this monograph,-|- that the ectocyst 

 in the genera Alcyonella and Plumatella sometimes presents upon its surface the appearance 

 of a transparent longitudinal furrow running along the length of each tube, commencing in 

 the vicinity of the orifice as a triangular notch-like space, and passing into a prominent keel as 



* In my Synopsis, published in the 'Annals of Natural History,' IS-tt, I recorded Alcyonella 

 stagnonim as a native of Ireland. The animal, however, there alluded to under this name is really 

 the Polype a Panache ; and I was led into this error from adopting at that time the opinion of llaspail, 

 Johnston, and other naturalists, that Trembley's animal was identical with the A. staynorum of 

 Lamarck. 



f Vide supra, p. 13. 



