22 



VERRILL ON THE POLYPS OF THE 



contracting into a broad, flattened cone. Walls smooth, destitute of suckers, pierced with 

 scattered cinclidte, thickened near the summit into a fold surrounding the column, above 

 this thinner and diaphanous. Disk broad, deeply folded or frilled at the margin. Tentacles 

 very numerous, the inner ones largest, scattered on the disk, the outer ones becoming 

 gradually very small and much crowded, fringe-like at the margin. Acontia very abundant, 

 but not emitted except after considerable irritation. The mouth has a broad and deep 

 groove at one angle and twelve to sixteen folds along each side. 



This genus as established by Oken had for its type Actinia dianthus of authors, the Euro- 

 pean representative of M. marginata. By Ehrenberg and several other writers the name 

 has been applied to Actinidce of entirely different characters, belonging to the Phyllactince, 

 thus excluding the typical species. We follow Milne-Edwards in retaining the name for 

 this genus, with 31. dianthus as its type. 



Metridium marginatum Milne-Edwards. 



Actinia marginata LeSueur, Journal Acad. Nat. Sciences Philad., vol. i. pt. i. p. 172 (1817). Gould, Report on Invertebrata of 

 Massachusetts, p. 349 (1841). Agassiz, Twelve Lectures on Comp. Embryology, p. 38, pi. xx. xxxii. xxxiii. (1849). Actinia 

 marginata. and Actinia dianthus? Stimpson, Synopsis of Marine Invert, of Grand Menan, p. 7 (1853). Actinia marginata Leidt, 

 Journal Acad. Nat. Sciences Philad., 2d series, vol. iii. p. 140 (1855). Metridium marginatum Milne-Edwards, Hist. Nat. des 

 Coralliaires, vol. i. p. 254 (1857). Actinia dianthus Dawson, On Sea-Anemones and Hydroid Polyps from the Gulf of St. Lawrence, 

 Canadian Naturalist and Geologist, vol. iii. p. 402, figs. 1 and 2 (1858). Actinia marginata Mrs. L. Agassiz, A First Lesson in Nat- 

 ural History, p. 10, figs. 1 to 6 (1859). Actinia marginata Agassiz, Contributions to the Natural History of the United States, vol. 

 iii. p. 39, fig. 8 (1860). 



The form of this species is very changeable ; in contraction it is hemispherical or a broad 

 low cone, sometimes almost disk-like ; in expansion most commonly like a thick cylinder 

 or pillar, higher than broad, with an expanded base, the summit surmounted by the broad, 

 elegantly frilled or undulated disk, with the tentacles drooping in a graceful fringe on all 

 sides and concealing the upper part of the column. Sometimes it becomes greatly elon- 

 gated and attenuated, the disk looking somewhat like a flower supported on its peduncle. 

 This form is most frequently assumed by young specimens. Column smooth, more or less 

 cylindrical, thickened near the top into a slightly elevated band or fold, which is about an 

 inch below the base of the tentacles in large specimens ; above this it becomes thinner and 

 diaphanous. Acontia emitted copiously from scattered cinclidae and from the mouth when 

 strongly irritated. They often extend to the distance of two inches or more. Disk much 

 broader than the column, its margin usually thrown into about twelve deep undulating folds 

 or frills, which are, however, quite changeable in size and number in the same individual. 

 Tentacles arranged on the outer half of the disk, leaving a central area free from them ; 

 the inner ones are scattered distantly and somewhat irregularly and are larger than the rest, 

 sometimes half an inch in length ; they decrease rapidly in size towards the margin, where 

 they become very crowded and quite small, looking like a delicate fringe along the edge. 



Color exceedingly variable, but most commonly with the column some shade of brown ; 

 the disk and column about the fold a light shade of the same, or flesh-colored ; the tentacles 

 grayish, often with lighter tips ; mouth similar in color to the column, but lighter. There 

 are, however, so many styles of coloration that it may be well to mention a few, though to 

 characterize all the variations would be scarcely possible. The following are often met 

 with : — 



1. Salmon-colored throughout ; tentacles a lighter tint of the same. 



2. Yellowish brown, streaked with lighter near the base ; tentacles delicate flesh-colored ; 

 mouth like the column. 



