GENUS NEBELA— NEBELA COLLAEIS. 151 



In all other respects, the forms agree with the varieties of N. collaris, hut I 

 have never met with specimens in which the shell was otherwise than com- 

 pressed. 



Mr. Carter, in the same work, described a form under the name of 

 Difflugia peltigeracea, which probably also belongs to the same animal as 

 Nebela collaris. 



The nature of the singularly varied shell of Nebela collaris I have not 

 been able to determine with any satisfaction. In the characteristic forms, 

 the elements of structure, the disks and plates, appear to be intrinsic, 

 and not of a foreign character. • They appear to be cemented together or 

 conjoined at the borders, and not implanted upon or incorporated with a 

 distinct chitinoid membrane. In breaking the shell, the line of rupture 

 follows the outlines or intervals of the disks and plates. The shell appears 

 to be silicious, as it remains unchanged when exposed to the action of 

 heated sulphuric and nitric acids. 



Dr. Wallich, in referring to the structure of the shell of the transitional 

 forms of Difflugia symmetrica, which, as previously intimated, I suspect to 

 belong to Nebela collaris, calls the peculiar elements colloid disks and plates. 

 He remarks of them that they are derived from the animal, and not directly 

 from the medium in which it lives. He supposes, however, that they are 

 formed through the coalescence of diatoms and other mineral elements 

 with the chitinoid basal substance of the shell, 

 which then undergo metamorphosis into all the 

 colloid forms that occur.* Of this process I have 

 been unable to satisfy myself; but the exceed- 

 ingly varied specimens which have come under 

 my notice, of shells composed of elements appar- 

 ently intrinsic and of regular but widely different 

 forms, of others apparently of extrinsic elements 

 regular and irregular, with many others of a transi- 

 tional character, would appear to justify the con- 

 clusion of Dr. Wallich. 



Since the foregoing went to press, in sphag- 

 num from the cedar swamp of Malaga, Gloucester County, New Jersey, 

 among multitudes of characteristic specimens of Nebela collaris, together 



"Annals and Mag. of Nat. Hist. 1864, xviii, p. 234, pi. ivi, figs. 27-33. 



Curved variety of Nebela collaris. 



