LOWER HELDERBERG ROCKS. 340 



AIITICULATA. 



ANNELIDA. 

 With the exception of the Tentaculites, which are arranged with the 

 CrinoideiB, I have no examples of authentic Annelida beyond the single 

 species of SpiRORBig figured on Plate uv. 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. 



Spiroi'bis laxns(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 striae 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 striae. The finer annulating strise are only 

 visible under a strong lens, and there are sometimes indications of fine spiral lines. 

 Fig. 18 a. A fragment of etone, preserving numerous individuals of this species. 

 Fig. 18 6. The upper side of the spire of a specimen, greatly enlarged. 

 Fig. 18 r. The lower side, showing the round mouth and the umbilicus. 



Fig. 18 </. 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 

 contiguons. (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. 



