134 



MANUAL OF ZOOLOGY. 



placed at the summit of a long, projecting tube, which is 

 termed the ' proboscis.' The ambulacral grooves in the Palaeo- 

 zoic Grinoids are found on the 

 ventral surfaces of the arms, 

 as in the living species ; but 

 instead of being continued 

 over the surface of the body 

 to the mouth, they stop 

 short at the bases of the 

 arms, where they gain ac- 

 cess to the interior of the 

 calyx by a series of special 

 apertures. (Billings.) 



More recently a stalked 

 Crinoid has been discovered 

 in the Atlantic -and North 

 Sea, and has been described 

 tinder the name of Wiizo- 

 crinus Lofotensis. The chief 

 interest of this form . is 

 the fact that it belongs to 

 a group of the Crinoidea 

 hitherto believed to be ex- 

 clusively confined to the 

 Mesozoic Rocks, viz. the 

 ApiocrinidoB or 'Pear-encri- 

 nites.' In fact, Rhizocrinus 

 is very closely allied to the 

 Cretaceous genus Bourgue- 

 ticrinus, and it may even be 

 doubted if it is generically 

 separable from it (fig. 36). 



In the second type of the 

 Crinoidea represented in 

 our seas by the Comatula, or 

 Feather- star the animal is 

 not permanently fixed, but is 

 only attached by a stalk when 

 young, in which condition it 

 was described as a distinct 

 species, under the name of Pentacrinus JEiiropceus. In its 

 adult condition, however, the Comatula is free, and consists 

 of a pentagonal disc, which gives origin to ten slender arms, 

 which are fringed with many marginal pinnule or 'cirri.' 

 The mouth and anus are on the ventral surface of the disc, 

 which in this case is again the inferior surface, since the ani- 



a - 



Fig. 36. Crinoidea : Rhizocrin us Lofoten sis, 

 a living Crinoid (after Wyville Thomson), 

 four times the natural size. a. Stem. 6. 

 Calyx, c c. Arms. 



