92 POTERIOCRINID^-rOTERIOCRINUS. 



two species of Poteriocrinus; Professor Pliilips by his researches increased the number 

 of known species to five ; and our own more recent inquiries have brought to light fifteen 

 well defined and interesting species, varying in size from the smallest radiated echmoderm 

 to the somewhat uncouth and massive P. crassus. 



The different species of Poteriocrinus do not appear to have been so abundantly 

 diffused throughout the carboniferous seas as some other genera, but in one particular 

 portion of the ancient sea bottom which was favourable to their mode of life, the bed 

 of the ocean must have been as thickly covered with them as a well-stocked garden is 

 witli plants. This ancient sea bed now forms part of the romantic scenery of Derby- 

 shire, and it is remarkable that the P. granulosus is the chief, if not the only species ' 

 found there; but this single species must have existed in such enormous profusion as 

 to form by its remains extensive and massive beds in which the broken and disjointed 

 columns are the principal, or rather the only constituent, and which indicate the vast 

 extent of time required for their accumulation. 



The specimens represented in PI. 9, fig. 1, 2 a, 4 a, 4 b, and 4 c, are in the cabinet of 

 Miss Rich, who has been indefatigable in collecting fossil cronoidea. 



