80 poteriocrinid^. — poteriocrinus. 



Formation and Localities. 

 Carboniferous limestone. — Yorkshire ; Hook Point, Wexford ; Port\ ille ? 



The radiatus is smaller than the conicus, and differs from it in having highly raised 

 radiating lines on the plates, which form a series of concentric triangles around the body. 

 The ray bearing plates are excavated in their centres for the attachment of the rays, these 

 excavations being narrow, the five primary rays which fit into them are less massive 

 than in most other species of Poteriocrinus. The rays are long, taper, and bifurcating 

 several times, the total number probably amounted to eighty. They are composed of 

 single series of joints as are all of the genus, but the articulations are shorter than in most 

 other species. Each joint has a single tentacula attached, but none of the crinoids with 

 single jointed rays can have the close set plumose tentacula which adds so much to 

 the beauty of those with the more complicated double jointed arms. 



The extraordinary length of the rays, measuring as they do in a small specimen up- 

 wards of four inches in length, together with the great distance between the bifurcations 

 distinguishes this species from most of its congeners. 



The proboscis is centrical, and the organ as is common to the genus is extremely large 

 and long as compared with the size of the body. It is covered with small hexagonal 

 plates, the mouth as in other species being situated at the apex. The column is similar 

 in structure to that of the P. rostratus. 



This species was discovered by the Authors in the Carboniferous limestone of Ireland. 



7. Species. Poteriocrinus Quinquangularis. (Atislin.) 

 PL 10, Ji(j. 2 a, 2 b, 2 c, 2 d, 2 e. 



Definition. — Dorso-central plates more attenuated than in the typical species. Mouth 

 proboscidiform and centrical ; main rays five, with one or more subdivisions ; column 

 enlarged and quinquangular near its attachment to the body and gradually becoming 

 circular as it recedes from it. 



