656 



THE WONDERS OF GEOLOGY. Lect. VI. 



surface granulated in a radiating manner, like those of 

 certain varieties of the Marsupite. In another genus, the 

 Cyathocrinites {Lign. 150), the receptacle is very simple, 

 and composed of but few plates : the ossicula of the columns 

 in the Actinocrinites and Cyathocrinites are round and 

 smooth : a beautiful specimen of the cup-shaped Encrinite is 

 represented, of half the natural size, in Lign, 150. 



44. Pentremites and Cystidea. — The species and 

 even genera of the fossil Crinoidea are so numerous, that 

 their bare enumeration would require more space than we 

 can allot to the subject, and I will only notice two of the 

 most remarkable types. 



Pentremites. These Lily-shaped animals seem to hold 

 an intermediate space between the Echinites and the 

 Encrinites. Their receptacle consists of five petaloid divi- 

 sions united by corresponding series of plates, which meet 

 in a point at the summit. Each petal is divided by a 

 groove, and is perforated near the apex. They have a 

 very short pedicle. These Crinoideans are so abundant 

 in some of the cherty beds of the mountain limestones of 

 Kentucky,* that the rocks have acquired the name of Pen- 

 tremital limestone. Seven species occur in the mountain 

 limestone of Yorkshire. 



Cystidea. In the oldest of the fossiliferous strata there 

 occur certain crinoideans, of a type which is supposed to 

 be restricted to the ancient palaeozoic periods. These 

 fossils are distinguished by Baron Von Buch by the names 

 of Cystidea. The receptacle is of an oval form, composed 

 of numerous polygonal plates articulated together, and 

 having the necessary apertures on the side of the cup 

 required by the economy of the animal ; it has a short 

 pedicle. The Cystidea are supposed to be destitute of true 

 arms, but some observers doubt the correctness of this con- 

 clusion ; they comprise several genera, and are the first 



* Journal of the Acad. Nat. Sciences of Philadelphia, for 1820. 



