448 PELMATOZOA. 



conical, or subcylindrical, and they generally resemble the Crinoids 

 in consisting of a stem or " column " and a body or " calyx." The 

 stem is sometimes long (as in Caryocrinus); but it is usually feebly 

 developed, and often attenuated towards its base, sometimes ter- 

 minating in a single long spindle-shaped piece {Lepadocrinus, fig. 

 326, d), in which case it probably did not serve as an organ of 

 attachment. In other cases the stem is rudimentary (as in Echino- 

 sphcerites) or it may be even absent altogether, the organism being 

 then mostly attached to foreign objects by the base of the calyx, or, 

 rarely, free. 



The calyx is composed of a number of polygonal plates, which 

 usually exhibit no marked radial disposition, though they are some- 

 times of limited number and arranged according to a definite plan. 

 In other cases the calyx-plates are indefinite in number and ar- 

 rangement ; and in some forms the number and arrangement of 

 the plates may be definite on one side of the calyx and indefinite 



Fig. 319. — Upper surface of the calyx of Glyptosphcerites Leuchtenbergi, from the Ordovician 

 rocks of Russia. m, Mouth, covered by the oral plates ; am, Ambulacra! grooves ; /, Socket for 

 one of the armlets ; an, Anus, without its covering-plates ; o, Supposed ovarian aperture. 



on the other. The base of the calyx is usually readily recognised 

 by the presence of the articular surface for the top joint of the 

 stem, or by being fixed to some foreign object ; and the upper sur- 

 face generally shows two or three openings, the nature and functions 

 of which have been much disputed. One of these openings is 

 central or subcentral in position (319, m), and is often protected in 

 well-preserved specimens with a covering of five small plates, repre- 

 senting the orals of the Crinoids, while it forms the point of con- 

 vergence of from two to five, simple or branched grooves which run 

 over the ventral surface of the calyx (am). These grooves clearly 

 correspond to the " ambulacral grooves " or " food-grooves " of the 

 Crinoids, and there can therefore be no doubt that the aperture in 



