32 VERRILL ON THE POLYPS OF THE 



and the other immediately surrounding the mouth, a tentacle in both sets arising from 

 each spheromere. Internal lamellae unequal ; one pair extending to the base or nearly so, 

 the others shorter, leaving a wide central cavity. 



This very peculiar group was first established by Milne-Edwards and Haime in 1852, 

 but with somewhat different limits from those now given. ll>/anthus was then included 

 with the typical forms, but has been separated more recently by Milne-Edwards. Gosse 

 has again united the two groups under the name Ih/anlhidw. The two families appear, 

 however, to be sufficiently distinct. 



For the present I prefer to include the genus Arachnactis in this division, although 

 possessing peculiarities which might possibly warrant the establishment of a distinct fam- 

 ily for it, as has been suggested by Mr. A. Agassiz. 1 But it seems quite doubtful to me 

 whether its adult condition has been hitherto observed, while the young of Cerianthus, 

 according to the observations of Haime, are free, swimming polyps. The structure and 

 arrangement of the internal lamellae and the two circles of tentacles are also similar. The 

 peculiarity of the development of the tentacles of Arachnactis, so well described by Mr. 

 Agassiz, seems also to have an intimate relation to the singular arrangement of the internal 

 lamella? of Cerianthus. It is also probable that the development of the tentacles in the 

 latter follows the same law as in the former. 



Genus Cerianthus Delle Chiaje. 



Moscata (?) Renier, Elements de Zoologie, partie 3, fasc. i. (1828). Cerianthus Delle 

 Chiaje, Descr. anim. inv. della Sicilia citeriore, iv. p. 124 (1841) ; Milne-Edwards and Haime, 

 Distr. methodique(1852) ; J. Haime, Memoire sur le Cerianthe (Ann. des Sci. nat., 4 me ser. 

 i. p. 341, 1854) ; Milne-Edwards, Coralliaires (1857). 



Column long, cylindrical, highly muscular and contractile, but not capable of involving 

 the disk ; form variable, but usually enlarged towards the disk, tapering slightly below to 

 the pointed or sometimes swollen base ; walls firm and strong, smooth externally, natu- 

 rally enclosed in a loosely investing and unattached tube composed principally of cast-off 

 lasso-cells, or nematocysts, forming a felt-like substance of considerable tenacity. Base 

 with a subterminal opening, serving for the expulsion and introduction of water. Tenta- 

 cles in both sets long, slender, very numerous, not contractile. Internal lamella? very un- 

 equal, one pair extending to the base, the others shorter and narrower, those opposite the 

 first pair smallest. The species, so far as observed, are hermaphrodite. 



Cerianthus americanus Agassiz, MS. 

 Cerianthus Agassiz, Proceedings of the Boston Society of Natural History, vii. p. 24 (1859). 



Column very long, cylindrical, expanded at the top, tapering gradually below; in expan- 

 sion, often two feet or more long ; in contraction, six or eight inches. Body enclosed in a 

 loosely investing tube, buried in the mud. Tentacles long and numerous, the outer series 

 (125 or more) are from 1.25 to 1.50 inches long, slender, very flexile, usually much curled 

 at the ends ; inner series similar, about .75 long, nearly the same as the former in appear- 



1 Journal of the Boston Society of Natural History, vol. vii. p. 529 (1SG3). 



