Haddon and Shackleton — A Revision of the British Actinice. 639 



flattened disc-like termination to the polyp, on which indistinct radii, usually 

 about 18 or 20 in number, can usually be discerned. The disc-like termination is 

 sensibly of greater diameter than the column of the polyp. 



Free Form. — The earliest stage we have seen consists of two polyps base to 

 base. These may divide by fission more or less symmetrically (PL lviii., figs. 5-1 1 ), 

 or one polyp may divide repeatedly, and the other not at all (PI. lviii., fig. 2—4). 

 The variations are so great that it would be impossible to attempt to describe 

 them all ; and we would here point out that the two species of Epizoanthus we 

 have examined which have free forms (viz. E. incrustatus, E. erdmanni) vary in 

 such a similar manner that the variations appear to have no taxonomic value ; the 

 same also holds good for E. abyssorum, Verr. We have seen specimens of 

 similar varieties of other species which have not as yet been identified ; one which 

 comes from Naples will, we believe, be found to be a free variety of E. arenaceus. 

 The size of the polyps and the character of the incrustations seem to be the only 

 external features which distinguish the free forms of these species from each other, 

 and these are obviously insufiicient. 



It is worthy of notice that the capitulum of the free varieties is usually less 

 flattened than that of the incrusting forms. 



The size which the polyps may attain apparently varies with the locality ; for 

 example, the largest of the Shetland specimens are 9 mm. in height, by 4'5 mm. 

 in diameter ; the largest colony from Balta measuring 30 x 20 mm. ; that from 

 Haaf being 35 x 20 mm. In the free variety the fully grown polyps average 

 6-7 mm. high, and 3— 3*5 mm. across ; the larger colonies being 22—23 mm. long 

 by 8—11 mm. broad. From the S. W. of Ireland, the polyps range up to 7*5 mm. 

 high by 3*5 in diameter, the carcinsecia being 24 x 15 mm. The W. of Ireland 

 specimens from oil Aran and from Donegal Bay run a good deal smaller : the 

 polyps average 3—6 mm. in height and 1*5— 3 mm. in diameter; most of the 

 colonies are quite small, the largest being 22 x 13 mm. The nature of the 

 incrustations also gives them a black-gray colour. The difference in size and 

 colour between these and more normal specimens is so marked as to constitute a 

 distinct variety. 



Verrill's original description (1866, p. 34) of this species (his Epizoanthus 

 americanus, n. sp.) is as follows: — " This species, which is parasitic on shells, has 

 an incrusting base, smooth and uniform on the lower side of the shell, but giving 

 rise to from fifteen to twenty polyps on the upper side, which diverge in all 

 directions. Polyps variable in height and size, those of the upper central portion 

 generally half an inch in height (13 mm.) and one-eighth (3"25 mm.) in diameter; 

 while those around the margin of the base are not more than half so large, and 

 much crowded. Base spreading over and completely investing dead shells of 

 Natica, Buccinum, &C.5 both externally and internally. The substance of the 



