LOWER HELDEKBEEG ROCKS. 191 



Edriociiiius pocillifonuis ( n. s.)- 



Plate V. Fia. 8 - 12. 



Base hemispheric or subturbinate, often less than a hemisphere, external- 

 ly smooth or finely granulate : upper margin scollopped with five 

 large and one smaller depression for the insertion of the radial and 

 anal plates. Interior more or less deeply concave, with depressions 

 corresponding to those on the edge of the cup ; the concavity not 

 parallel to the exterior convexity. Radial plates and arms unknown. 



This small sj^ecies occurs iu considerable numbers in the central part of the shaly 

 limestone, varying in size from that of half a pea to more than lialf an inch, and 

 of greater proportional diiferences in elevation. A few retain some evidence of their 

 former attachment to other bodies, but for the most part they are quite smooth upon 

 the exterior. This part of the crinoid appears to be composed of an exterior and an 

 inner plate; the inner not corresponding with the outer one in its concavity, the 

 exterior form being given by the process of separation from its sedentary position, 

 and the subsequent secretion of calcareous matter to form a smooth surface. In some 

 instances the interior presents scarcely any appreciable concavity, and the entire 

 basal portion is then much wider than high. 



These bodies are usually so small as to be overlooked, or regarded as unimportant 

 fragments of crinoids; and are rarely seen in collections. 



Fig. 8. Basal view of a large individual, the proportional length being greater than usual. 



Fig. 9. Lateral view of the same. 



Fig. 10. Lateral view of a larger specimen. 



Fig. 11. Interior of the same. 



Fig. 12. Enlargement of the concavity of fig. 10, showing the depressions corresponding to 

 the depressions in the margin and the concentrically striated surface. At each 

 angle there is a slight depression or pore, which seems to communicate with the 

 cavity between the basal and inner plate. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 

 group : Helderberg mountains, Albany county. • 



[ PALiEONTOLOOT III.] 16 



