EASTERN COAST OF THE UNITED STATES. 



21 



distended. Walls thin, parchment-like, the upper half covered by large, prominent, ad- 

 hesive verrucco, concave at their summits, arranged rather closely in vertical rows, becom- 

 ing obsolete below. The rows are separated by wider naked spaces ; margin with a 

 thickened fold, below which there is a circle of large compound verrucae, which are the 

 uppermost ones in the vertical rows of suckers ; these are short, thick, distinctly trilobed 

 on the lower side, each lobe again divided below into short rounded tubercles or crenula- 

 tions. Tentacles very numerous, short, thick, pointed, arranged in many rows ; the twelve 

 inner ones, belonging to the first two cycles, are thicker than the rest, six of them gener- 

 ally curved inwards in expansion, and six erect ; the outer ones are more slender, scarcely 

 shorter, and are generally carried spreading outward ; mouth with two opposite crescent- 

 shaped folds. 



Color brownish gray or greenish brown, with lighter longitudinal lines ; disk similar to 

 the column, with darker radiating lines, and a lighter space around the mouth ; tentacles 

 yellowish green, with a dark brown median line on the inner side, interrupted by several 

 white spots, which often blend into a white line near the base ; verrucse gray. 



Height in expansion often 6 inches ; greatest diameter 1.35 ; length of tentacles about 

 .30. (Coll. Mus. Comp. Zool.) 



Charleston, S. C, buried to the tentacles in sand (L. Agassiz) ; Fort Macon, N. C. (Sam'l 

 Cabot) ; Beaufort, N. C. (A. S. Bickmore). 



Sub-family Sagartid^e. 

 Family Sagartidce Gosse, Actinologia Britannica, p. 9 (1860). 



This division has been established by Gosse on the character of having openings like 

 loopholes (cinclidce) piercing the walls, through which peculiar thread-like organs, consisting 

 in great part of lasso-cells, are thrown out for defence when irritated, and possibly, in some 

 cases, for the purpose of obtaining food. These thread-like organs are often, also, thrown 

 out from the mouth and accidental ruptures of the walls in great numbers. When pro- 

 truded for self-defence, they are slowly withdrawn again, if the exciting cause be removed. 

 This I have observed in Metridium marginatum, and Gosse mentions the same fact in respect 

 to other species. The mode in which the threads are expelled and withdrawn seems to be 

 entirely mechanical, depending upon the flow of water through the cinclidce, the force of the 

 current impelling the flexible filaments either outward or inward according to its course. 



There are a few additional characters which separate this group from other Actinidce, 

 though mostly of a negative nature, and at the same time it is somewhat doubtful whether 

 cinclidce and acontia are not present in other divisions, namely, Actininice, Antheidce, and, pos- 

 sibly, Biinodidce. 



Genus Metridium Oken. 



Actinia (pars) Linn^us, Pennant, Ellis and Solander, Lamarck, Cuvier, etc. Meiridhmi 

 Oken, Lehrbuch der Naturgeschichte, iii. p. 349 (1815). Actinoloba (pars) Blainville, Diet, 

 des Sci. Nat. and Manuel d'Actinologie, p. 322 (1830-34). Cribrina (pars) Ehrenberg, Corall. 

 des rothen Meeres (1834). Sagartia (pars) Gosse, Manual Mar. Zool. Actinoloba Gosse, 

 Actinologia Britannica, p. 11 (1860). 



Column very contractile and changeable in form, often much elongated, but capable of 



MEMOIKS BOST. SOC. NAT. HIST. Vol. I. 6 



