CRINOIDEA. 



281 



of radials. There are six inter-radials in each inter-radial 

 space, and seven or more anal plates. The arms are well 

 developed, the column is annulated or moniliform, and the 

 plates are usually ornamented with radiating ridges (fig. 166). 



In the little Devonian family of the Gfasterocomidce, as 

 represented by Gasterocoma ( EpactocrinuJ), there are five 

 basals, surrounding the uppermost joint of the column, and 

 succeeded by a single cycle of five radials, the upper edges 

 of which are hollowed out for the reception of the brachial 

 grooves on their way into the interior of the calyx. The 

 anus is quite excentric, and is placed just 

 above one of the five basals, surrounded 

 by a ring of five small plates, surmounted 

 by a sixth larger one. There are five arms ; 

 and the column is obtusely quadrangular, 

 and is perforated by four canals, surround- 

 ing, or confluent with, a larger central 

 tube. 



In the Gupressocrinidce, as represented 

 by the singular Cupressocrinus of the De- 

 vonian, the calyx (fig. 167) is cup-shaped, 

 the centre of its base being formed by the 

 expanded uppermost joint of the column, 

 which is surrounded by five basals, which 

 carry a single cycle of five large radials. 

 These support five much smaller plates, 

 which may be secondary radials, and these 

 give origin to the five arms. The arms 

 are undivided, diminish gradually towards 

 their apices, and by the accurate apposition 

 of their edges form together a pentagonal 

 pyramid, when the animal is at rest. The 

 arms are deeply grooved on their ventral 

 surfaces, but these grooves are roofed 

 over by four parallel rows of small cal- 

 careous plates, which leave centrally a 

 small ambulacral sulcus. The upper sur- 

 face of the calyx appears to have been covered with a 

 leathery perisome ; the mouth is central, and the anus ex- 



liliiformis. 



Encrinus 

 Muschel- 

 kalk. The lower figure 

 shows the articulating 

 surface of one of the 

 column-joints. 



