38 P. H. OAEPENTEE ON COMATTTL^ FEOM 



within the centrodorsal piece into the chambers of the so-called 

 *' heart." They cannot therefore have entered the lower open 

 ends of the radial pits, which usually lie altogether outside the cen- 

 trodorsal cavity (see Schliiter's description of them in Ant. Betzii, 

 p. 44) ; hut they must have entered this cavity hy the more central 

 part of the dorsal star, leaving the outer ends of its rays to the 

 radial extensions of the coelom. This condition may possibly have 

 existed in such forms as Ant. semiglohosa and Ant. Retzii, which 

 seem to have retained their stem till a very late period of growth, 

 like the recent Ant. Sarsii, as there is a very large dorsal star. 



But other fossil species, such as Ant. lettensis and Solanocrinus 

 scrohimlatus, resemble recent Comatulce in retaining no permanent 

 traces of the attachment of a stem. "We may conclude from this 

 that the separation from their stem took place at an earlier period 

 of development than in the case of A. Retzii, &c. Por such forms 

 as these Schliiter's statement does not hold good; the closure of 

 their radial pits below does not result from the obliteration of the 

 original dorsal star. Thus in Ant. rosacea this star disappears at a 

 very early period of growth, long before either it or the centrodorsal 

 piece itself reaches any thing like the size that they have in A. semi- 

 glohosa, A. Retzii, or A. 'paradooca. This is well seen in pi. xli. 

 fig 2 of Dr. Carpenter's memoir* on this type. The dorsal star is a 

 minute opening in the floor of the wide basin-like cavity of the im- 

 mature centrodorsal piece, the side walls of which bend inwards 

 very slightly at the points where the radial pits would subsequently 

 appear. The calcareous tissue which closes the dorsal star in the 

 centre of the floor of this cavity must therefore be entirely distinct 

 from that underneath the later-developed radial pits, which is a part 

 of its side walls. Were this absorbed, and the pits thereby rendered 

 sufficiently deep to perforate the lower surface of the centrodorsal, 

 they would do so between the ends of the rays of the dorsal star 

 (supposing it to persist) and the circumference of the plate ; and 

 the union of such openings with the rays would give the appear- 

 ance of a relatively large star, just as in A. semiglohosa. There are 

 other fossil species, such as Ant. sulcata and Act. Miilleri (PI. Y. 

 fig. 6), which resemble most recent Comatulce in having neither radial 

 pits nor dorsal star on the centrodorsal piece. 



Schliiter's description of Ant. lenticularis contains the following 

 passage (p. 46) : — "The dorsal pole is slightly concave and shows a 

 small distinct star, which indicates the presence of radial pits on the 

 upper surface of the centrodorsal." On p. 48 he points out that 

 there is no dorsal star in Ant. italica, but only a simple round hole. 

 " The nutritive canal of the stem was therefore not lobate, as in A. 

 lenticularis, but round, which also points to the absence of radial 

 pits." 



The last sentence refers to the shape of the opening in the middle 



of the upper surface of the centrodorsal piece, which was formerly 



regarded as the mouth. It surrounds the upper ends of the 



chambers of the so-called "heart," which occupies the central 



* Phil. Trans. 1866, vol. 156. 



