Ch. XXV.] FOSSILS OF THE MOUNTAIN LIMESTONE. 



Fig. 567. Fig. 563. 



517 



Cyathocrinites planus. Miller. 

 Body and arms. Mountain 

 Limestone. 



Cyathocrinus caryocrinoides, M'Coy. 



a. Surface of one of the joints of the stem. 



b. Pelvis or body ; called also calyx or cup. 



c. One of the pelvic plates. 



In the greater part of them, the cup or pelvis, fig. 568 b, is greatly 

 developed in size in proportion to the arms, although this is not the 

 case in fig. 567. The genera Poteriocrinus, Cyathocrinus, Pentremites, 

 Antinocrinus, and Platycrinus are all of them characteristic of this 

 formation. Other Echinoderms are rare, a few Sea-TJrchins only being 

 known : these have a complex structure, with many more plates on 

 their surface than are seen in the modern genera of the same group. 

 One genus, the Palcechinus (fig. 569), is the analogue of the modern 



Fier. 569. 



Fig. 570. 



Palcechinus gigas, M'Coy. Eeduced. 



Mountain Limestone. 



Ireland. 



Productus semireticulatits, Martin, sp. 

 (P. antiquatus, Sow.) Mountain Lime- 

 stone. England ; Eussia ; the Andes, &c. 



Echinus. The other, Archceocidaris, represents, in like manner, the 

 Cidaris of the present seas. 



Of Mollusca the Brachiopoda (or Palliobranchiates) constitute the 

 larger part, and are not only numerous, but often of large size. Per- 

 haps the most characteristic shells of the formation are large species 

 of Productus, such as P. giganteus, P. hemisphcericus, P. semireticulatus 

 (fig. 570), and P. scabriculus. Large plaited spirifers, as Spirifer stria- 

 tics, S. rotundatus, and S. trigonalis (fig. 571), also abound; and 

 smooth species, such as Spirifer glaber (fig. 572), with its numerous 

 varieties. 



The family of the brachiopoda to which these shells belong, is far 



