24 BRITISH FOSSIL CORALS. 



concave track, and the mouth projects in the form of a more or less oblong truncated 

 cone. There are from sixteen to eighteen internal folds, faintly shown, however, on the 

 rim around the mouth. 



" The tentacules are of the same number as the septa whose summits they envelope, and 

 there are always from thirty-two to thirty-six. They are evidently equal in size and in 

 length. Their length is nearly equal to that of the diameter of the corallite. They 

 are elongated, swelling a little above their insertion, and then becoming very slender as far 

 as their free extremity, which is terminated by a small knob-shaped enlargement. 



" The polypes can contract to various extents. Several very characteristic movements 

 may be noticed, however. A slight agitation of the surrounding water or the contact with 

 small particles, suflices to cause a shortening of some or all of the tentacules, although the 

 disc does not alter its shape or position. 



" When the exciting cause acts more decidedly and continuously, the shortening of the 

 tentacules increases, the disc retreats, and the protractile mouth elongates in advance of the 

 calice. This state of things is very usual in disturbed or decomposing water. If the 

 animal itself is shaken or is touched, it retracts its disc into the calicular fossa, and 

 nothing is to be seen of the soft parts but some small elevations corresponding with 

 the tentacules. Finally, a violent shock or a prolonged irritation produces so complete a 

 retractation that the tentacules disappear completely, and the white colour of the septa is 

 seen. The calice looks as if it were dried, and there is only a light brown tissue in the 

 interseptal loculi. In this last case the water which usually distends the tissues has been 

 gradually expelled, and they are so reduced in volume that they are readily Avithdrawn 

 into the interseptal and columellar spaces. 



" The disc and the tentacules are of a transparent brown colour, and when the sun 

 shines, a brilliant green tint may be seen within the tentacules. This coloration evidently 

 depends in some instances upon the light. But it is necessary to remark, that the 

 primary and secondary tentacules and those of the third cycle which are flanked by 

 quaternary are those which show this green tint in their insides. The peculiarities of these 

 tentacules coincide with the presence of pali, which are situated beneath and withiu them. 



" When the mouth opens, as it often does when the polype is semi-retracted, the 

 papillae of the columella are visible. The stomach is very short, and is almost reduced to 

 a rim, which is confounded with the lips. 



" The tentacules are not smooth, but are covered with a multitude of small wart-shaped 

 prominences, of a transparent white colour ; they are equal in size, and measure a tenth 

 of a millimetre in width. The terminal bulb presents a narrow central canal, which 

 communicates both with the tentacular cavity and with the external medium. The 

 three layers of tissue which constitute the tentacules have the same general characters 

 as in the Adinice, but the fom- layers of the tegumentary covering are not to be 

 detected. 



"1. The first envelope is quite transparent, and is composed principally of nematocysts of 



