COMPARATIVE ANATOMY OF SOME BRITISH ACTINLE. 543 



while immature ones are embedded in the middle of the ectodermal 

 tissue and are deeply stained. The older ones are longer and more 

 transparent. The spiral thread could be faintly distinguished in one or 

 two cases ; it is very fine and has a large number of coils. The nemato- 

 cysts are more numerous at the tip, but they are well developed along the 

 stem. 



A. alfordi and A. gelam are alike in the following respects : they have 

 more than six pairs of perfect mesenteries ; they possess a well-circum- 

 scribed endodermal muscle. I therefore suggest the following as an 

 amended definition of Anthopleura : Cribrinidse with the upper portion 

 of the column wall provided with longitudinal rows of verrucae, the lower 

 portion being smooth. The margin forms a more or less distinct collar 

 and the tentacles are polycyclic and entacmseous. More than six pairs 

 of mesenteries of the first cycle are perfect. 



Corynactis viridis (Allman, 1846). 

 Classification : The following is the classification adopted by Haddon : — 



Tribe : Hexactinise (Hertwig, 1882). 

 Order : Stichodactylinae (Andres). 

 Sub-order : Homodactylinse (Duerden). 

 Family : Corallimorphidse (Hertwig). 

 Genus : Corynactis (Allman). 

 Species : viridis. 



Haddon gives the following definition of the Stichodactvlinse : " Hex- 

 actinife in which more than one tentacle may communicate with a 

 mesenterial chamber. Usually a peripheral series of one or more cycles 

 can be distinguished from an inner accessory series, the members of which 

 are radially arranged or in groups, and are of different form. The sphincter 

 muscle may be endodermal or absent." Branched tentacles appear quite 

 often, 



Duerden has divided the Stichodactylinne into two sub-orders : — 



(a) The Heterodactylinse in which the tentacles are of two kinds, 

 usually marginal and accessory, and separated by a bare portion of the 

 disk, e.g. Actinotryx, Khodactis, Heterodactyla. 



(6) The Homodactylinae in which the tentacles are of one kind, simple 

 or complex, and usually follow one another in continuous rows, e.g. 

 Richordea, Corynactis, Stoichactis. 



Family : CoraUimorphidse. Stichodactylinae with a marginal corona 

 of tentacles, and accessory tentacles, arranged in radial series each con- 



