LOWER HELDERBERG ROCKS. 
349 
ARTICULATA. 
ANNELIDA. 
With the exception of the Tentaculites, which are arranged with the 
Crinoideee, I have no examples of authentic Annelida beyond the single 
species of Spirorbis figured on Plate liv. The obscure trails or tracks 
sometimes noticed in the lower part of the group are not sufficiently 
characteristic to be of value in the determination of the strata, or to 
furnish any reliable information regarding the animals which produced 
/ 
them. 
Spirorbis tans (n. s.). 
Plate LIV. Fig. 18 a - e. 
Shell discoid or spirally ascending, dextral, consisting of about three 
volutions (varying from two and a half to four), which are conspicuous 
on the upper side, and partially exposed in a deep umbilicus : tube 
round, gradually enlarging towards the aperture ; aperture round, often 
turned at right angles to the spire, and sometimes a part of the last 
volution, or the entire volution, is quite free and extended in the same 
manner, having a slightly spiral direction. 
Surface marked by strong annulating ridges, and by finer strim in the 
spaces between. 
This species assumes a considerable variety of appearance; but the numerous 
gradations between those having all the volutions contiguous, and those where the 
last volution is entirely free, leave no doubt that all the varieties observed are of a 
single specific form. The transverse ridges are usually conspicuous, but these some¬ 
times appear as closely arranged lamellose strirn. The finer annulating strife are only 
visible under a strong lens, and there are sometimes indications of fine spiral lines. 
Fig. 18 a. A fragment of stone, preserving numerous individuals of this species. 
Fig. 18 b. The upper side of the spire of a specimen, greatly enlarged. 
Fig. 18 c. The lover side, shoving the round mouth and the umbilicus. 
Fig. 18 d. A specimen in which the last volution is free. (This is a common condition of the 
species ) 
Fig. 18 e. A specimen in which the apex is closely involved, and the remaining portions not 
contiguous. (This is an extreme form, and rarely seen.) 
Geological position and locality. In the tentaculite limestone, base of Helderberg 
mountains : Schoharie, Carlisle, and other places. 
