VERRILL, SYNOPSIS OF POLYPS AND CORALS. 51 



minute transverse tubercles, and a pair of larger ambu- 

 latory tubercles are situated on each ring. The respira- 

 tory tube is simple, not divided ; - the filiform simple 

 terminal portion being about ' as long as the whole tube. 

 Length of the whole body .90 ; of the tube .48 inch. 



NOTE. The excellent drawings illustrating this paper .were made 

 by Mr. J. H. Emerton. My description of the mouth-parts of Chiron- 

 omus (Fig. 1.) were taken from his drawings, made from the larva 

 when alive. The drawings of Chironomus and details were all made 

 from living specimens. 



IV. Synopsis of the Polyps and Corals of the North 

 Pacific Exploring Expedition, under Commodore C. 

 Ringgold and Copt. John Rodgers, V. S. N., from 

 1853 to 1856. Collected by Dr. Wm. Stimpson, 

 Naturalist to the Expedition. 



BY A. E. VERRILL. 



PART IV. ACTINARIA. With three Plates. 

 [ Continued from Vol. V, p. 330. ] 



SUBFAMILY, SAGARTIN.E Verrill. 



Family, Sagartiadce Gosse, 1858; Actin. Brit., p. 9, 1860. 



Column perforated by small openings (cinclidae) from 

 which long slender filaments (acontia) are emitted, more 

 or less abundantly, when unusually irritated. These 

 acontia are chiefly composed of nettling organs, and appear 

 to serve as organs of defence. They are withdrawn after 

 the disturbance has ceased. Surface of column either 

 smooth or with minute contractile suckers. Tentacles 

 numerous, usually slender and pointed, diminishing in 

 length towards the margin ; very contractile, like the disk 

 and column. 



METRIDIUM Oken. 



Metridium Oken, Lehrbuch der Naturg., Ill, p. 349, 1815 (non 

 Ehrenberg, 1834, Dana, 1846, Gosse, I860.) 



