EASTERN COAST OF THE UNITED STATES. 13 



surface of the frond nearly smooth, but marked with fine radiating stripe, filled with 

 small spicula, and with a net-work of light-colored lines. Cells few, rather large, sur- 

 rounded by small and slightly prominent spicula; rudimentary individuals numerous, 

 irregularly scattered among the cells, a little prominent, composed of eight or ten little 

 lobes. 



Color of the disk, when living, according to the drawings of Prof. Agassiz, a vivid 

 reddish purple ; peduncle the same color, except at the tip and the point of union with 

 the disk, where it is lighter ; polyps diaphanous, delicate bluish white, the walls with 

 specks of brown and a circle of brown spots just below the tentacles ; tentacles diaph- 

 anous with a marginal line of brown on each side, widening towards the base. 



The polyps are arranged symmetrically on each side of a narrow naked space, extend- 

 ing from the sinus more than half across the disk, and situated above the large central 

 chamber within ; when expanded they are much exsert, but less so than in other spe- 

 cies of the genus. The tentacles are narrow lanceolate, with rather distant, long lobes, 

 which are confined principally to the outer half. Mouth oblong, with four small rounded 

 lobes on each side. 



This species is capable of distending itself greatly with water, when it becomes very 

 thick and swollen, thinnest at the edges ; the peduncle can expand to four or five times 

 its length when contracted. According to Prof. Agassiz, who has carefully studied it 

 while living, 1 it is remarkably phosphorescent, emitting a " golden green light of a most 

 wonderful softness." Its ordinary position when expanded is to have the peduncle buried 

 perpendicularly in the sand and swollen into a bulb at the end. In locomotion the disk 

 itself can be used, either by alternately contracting and expanding the two lateral por- 

 tions, or by expanding and extending the anterior end and then contracting so as to 

 form a transverse constriction which gradually passes oft' posteriorly. (Coll. Mus. Comp. 

 Zool.) 



It is found quite commonly at low-water mark and in pools left by the tide on the 

 coast of Georgia and South Carolina, extending as far northward as Beaufort, N. C. 



Order II. ZOANTHAKIA. 



The structural features which characterize this order are principally the combination 

 of the spheromeres in multiples of six, and the presence of interambulacral spaces be- 

 tween them, in which the new spheromeres are developed during growth, together 

 with the simple tubular structure of the tentacles, which vary in number from twelve 

 to several hundred. 



The lateral walls of the spheromeres, forming radiating partitions, of which the 

 principal ones extend from the outer wall to the digestive sac, have been called lamrflce 

 by Dana, and septa by some later writers ; but since the latter term has been definitely 

 applied by Milne-Edwards and Haime to the solid plates formed, in many genera, 

 within the spheromeres, between the lamella', it ought to be used in this sense alone. 



Owing to the great advance made in our knowledge of the structure of this group 

 within a comparatively recent time, through the careful investigations of Dana, Milne- 

 Edwards and Haime, and others, the number of terms that must necessarily be employed 

 in the description of their parts has been greatly increased, but, in order to avoid con- 



1 Proceedings of the American Association, 1850. 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. 4 



