106 



tocystites and three in most of the other genera of the group. Neither m 

 the plates nor in the hydrospires is there exhibited any tendency to a ra- 

 diated arrangement. The most ancient genus of this family is Ghjptocys- 

 titeSj which first appears in the Chazy limestones and seems to have 

 become extinct in the Trenton. The other genera occur in various hori- 

 zons between the Chazy and the Devonian. | 



In the genera Hemicosmttes and Caryocrmus the hydrospires in the 

 upper part of the test converge toward, but do not reach, the central 

 point of the apex, thus forming the commencement of that concentration 

 and complete radiation which is exhibited in the ambulacral canal system 

 of the higher echinoderms. In a former note (ante p. 98) itispointed out 

 that Caryocrinus has thirty hydrospires — ten at the base with their long- 

 er diagonals vertical, — a zone of six round the middle with their diagonals 

 horizontal, and a third band of fourteen around the upper part of the fos- 

 sil. These latter are represented in fig. 61, as if spread out on a plane 

 surface. On consulting this figure it will be seen that the flat tubes of the 

 hydrospires, represented by the parallel lines, all converge toward the> 

 central point from which the dotted lines radiate. This point is the posi- 

 tion of the mouth in the recent echinoderms, but in Caryocrinus it is occu- 

 pied by a large soUd imperforate plate. The hydrospires are arranged ia 

 five groups. Commencing at m v and going round by 1, 2, &c., there 

 are four in the first group ; one in the second ; four in the third ; one in 

 the fourth atid four in the fifth. These five groups represent the five am- 

 bulacral canals of the recent echinoderms. In the specimen from which 

 ^his diagram was constructed there are the bases of fifteen free arms to be 

 seen situated at the outer extremities of the dotted lines. At the base of 

 each arm there is a small pore, j;, which I beUeve to have been exclusive- 

 ly ovarian in its functions. The hydrospires have no connection what- 

 ever with the arms, and are, moreover, all of them entirely separated from 

 each other. If then they represent the ambulacral system of the recent 

 echinoderms, it is quite certain that that system was at first, (or in the 

 undeveloped stage in which it existed in the Cystidea,) destitute of the 

 oesophageal ring. 



In Codaster a further concentration of the respiratory organs is exhibi- 

 ted. There are here only five hydrospires, and they are all confined to 

 the circle around the apex. Two of them are incomplete in order to make 

 room for the large mouth and vent {m v, 65.) They are each divided into 

 two halves by an arm, al, rt2, &c. They are only connected with the 

 arms to this extent, that these latter lie back upon them. The arms are 

 provided with pinnulie, but it is not at all certain that they (the pinnulae) 

 were in any direct communication with the hydrospires. It is evident 



