21 



On closer examination the mandible appears (fig. 3D) to consist of a middle-part occu- 

 pying the whole of its length, the proper mandible, and two side parts. The middle part is 

 in the whole of its length slightly and evenly curved inwards; in its lower or basal part, thicker; 

 and upwards, or towards the free end, gradually thinner being a strong or hard chitinous 

 plate of narrow lancet-like shape pointed at the extremity, truncated at the basis and forming 

 a transversal straight line, or properly a thickened stripe with which the mandible is movably 

 inserted in the distal, likewise straight edge of the receptacle, and of which both the side- 

 borders are slightly concave. These borders are of a horny-yellow color, and thickened or 

 like fillets, particularly the basal border, while the side-borders become gradually thinner 

 towards their superior part. Both the side-parts of the mandible are on the contrary extre- 

 mely thin, membranous, somewhat soft and hyaline; they surround the sides of the middle 

 part, and also its point like a broad brim, and their border is nearly straight or slightly 

 convex, and at the extremity of the mandible where they join, evenly curved. After dessica- 

 tioii the mandible retains its shape completely, its chitinous stripes retaining their horny- 

 yellow color, and is distinguished from the nearly dull cells by its shining surface. 



The animal (the ,,Polypide" Allman) (fig. 28 b. fig. 30) is entirely colorless and trans- 

 parent with slightly yellowish intestinal region; and the mouth is surrounded with a circle 

 of 24 tentacles. On the slightest irritation, the animal withdraws itself as usual with the 

 Polyzoa, rapidly, one might almost say quick as lightning, and with a jerk into its cell. 



The mandible of the avicularia is found extended in various positions: sometimes more 

 or less obliquely upwards and outwards from the colony (see fig. 27. a. a.) sometimes straight 

 out from it (fig. 26) and finally sometimes curved downwards or backwards (fig. 26. fig. 28 a.) 

 The last position is the most usual-, when the animals of the colony are in a state of full 

 undisturbed tranquility. In case of irritation the mandible is curved somewhat rapidly upward, 

 and is laid close up to the cell of the avicularium which it then exactly covers (fig. 25. a.a.) 

 The opening or extension of the mandible seems to take place still more rapidly and ener- 

 getically than its closing. A loose colony, or one separated from its attachment, lying on the 

 bottom of a vessel filled with sea water, was even observed to move a little way, or as it 

 were to make a leap, by the combined effort of the mandibles of all the avicularia, as they, 

 by rapidly and energetically opening themselves, and curving outward and downward, pressed 

 against the bottom of the vessel. 



The present species, which occurs somewhat rarely in Lofoten at the depth of 120 

 fathoms (at Guldbrands0er) to 300 fathoms (at Skraaven) is distinguished, as has been shewn, 

 from the hitherto known species ofFlustra, principally by its avicularia and especially by the 

 great size and peculiar form of the mandible. 



The largest avicularia (and those most resembling the animals' cells) which are hitherto 

 known, are found in the Flustra Barlei Busk (F. membranaceo-truncata Smitt). Where they 

 are of Y 3 Va the size of the animals' cells, and in F. foliacea Linne, where they are nearly 

 equal in size to the cells. Both these species have however a quadrangular receptacle, and 



