Von Buch on Crinoidea. 



15 



of the vertex, appear to terminate in three small processes or 

 arms which are pierced, and might perhaps form distinct 

 oval apertures. No anal aperture is evident. The great regu- 

 larity of this arrangement is still more evident from the great 

 elegance with which prominences are distributed in series 

 over each assula of thorax and vertex. They proceed on the 

 costals from the centre to the upper angle of the hexagon, 

 none towards the lower. On the vertical assulae, on the con- 

 trary, these series go towards the lower angles, none towards 

 the upper. Only the halves of the surfaces are decorated in 

 this remarkable manner. The vertical and lateral series thus 

 combine to form a highly elegant wreath environing the 

 whole figure. These warts or prominences are pierced in 

 the centre, and appear to be points of adhesion for spines. 

 The central series of each assula is double. On the other 

 parts of the assular surface there are but few similar warts 

 scattered without any order. 



Cryptocrinites regularis and C. Cerasus (Pander, t. ii. 

 f.24. n. 26.). 



The pelvis is that of a Platycrinites, the thorax that of a 

 Poteriocrinites; but the vertex is still closed, and without arms. 

 However, five ribs or rings extending from the lower extre- 

 mity to the vertex are hidden beneath the assulae, which are 

 thus raised exactly in the form of a roof, just as may be 

 observed in Actocrinites before the arms divide. The es- 

 sential character of the Crinoidea exists, therefore, almost 

 entirely in the Cryptocrinites, but it is yet hidden in the 

 interior. The pelvis consists of three plates, which are 

 united to form a pentagon, an arrangement which again 

 occurs in Platycrinites, in Rhodocrinites, and in Actocrinites, 

 but only in the older ones; in the later Jura Crinoidea 

 it is no longer found. The thorax is surrounded by Jive 

 costals, and the vertex likewise by five plates, which alter- 

 nate with the costals. Minute plates surround the mouth, 

 which is for the most part open. Between the vertex and 

 costals there is again a large aperture covered by five valves. 

 In Cryptocrinites Cerasus, intercostals are, moreover, situ- 

 ated on the original five of the thorax, thus somewhat dis- 

 turbing the regularity of the upper half ; and there are also 

 probably more than five assulae or plates on the vertex. The 

 side on which the valvate aperture is situated is bulged out 

 at all points ; the effort of the hidden arms to break through 

 the sides is here evident. The size of these animals sel- 

 dom exceeds that of a pea ; the petiole which bears it has 

 the thickness of a pin. Hitherto they have occurred solely 

 in the hills near St. Petersburgh. 



