1881.] NATURAL SCIENCES OF PHILADELPHIA. 207 



seen that the hydrospires above noted, and those of the Blastoids, 

 have not only a similar form, but also a very similar position.^ 



The hydrospires of the Crinoids, like those of the Blastoids, are 

 placed in close proximity to the arms with which they were 

 probably in communication, close to the test and within the general 

 cavity of the body. 



The above is, to our knowledge, the only case in which hydro- 

 spires have been observed among the Sphaeroidocrinidae, but thej^ 

 were probably present in other genera, and perhaps in the Palseo- 

 crinoids generally- ; while these organs are unknown in all later 

 and recent Crinoids, and in other groups of Echinoderms. 



It is a fact worthy of note that all Cystideans and Blastoids, 

 and so far as known, all Palaeocrinoids which possess hydro- 



' The vault in the Blastoids, as we understand it, consists not merely of 

 the plates which cover the oral opening, but extends all along the median 

 portions of the pseudambulacra (PI. XIX, fig. 3), "forming underneath a 

 good-sized tunnel, which we take to be the bomologue of the ambulacra! 

 tube of the Crinoids. If this interpretation is correct the structure bears 

 the closest similarity to that found in those Crinoids in which the vault is 

 extended into free rays, and in which these extensions combine to some 

 degree the characters of. the arms and body. The recumbent arms of the 

 Blastoids are, according to this, lateral extensions of the body which 

 take the place of true arms ; but while in the Crinoids the radial exten- 

 sions give off regular arms, in which the ambulacral tubes are converted 

 into grooves, the corresponding parts in Blastoids remain attached to the 

 body, and the pinnules form the only free appendages. It is possible, how- 

 ever, that in the Blastoids the lateral furrowswhich traverse the ambulacral 

 fields were not covered by plates, and that these correspond to the open 

 arm grooves — respectively arms— in Crinoids. 



Dr. Hambach (Contributions on the Anatomy of the genus Pentremites, 

 p. 7) is probably correct in supposing that the pinnules of the Blastoids 

 were not connected with the pores, as hitherto believed. We think it 

 probable that they rested in the funnel-shaped pits which alternate with 

 the pores, and which communicate with the lateral grooves of the pseud- 

 ambulacra, while the pores probably communicated with the hydrospires. 

 This view coincides with what we have heretofore suggested, that the upper 

 face of the pseudambulacra corresponds to the grooves within the arms of 

 the Crinoids. and indicates that there are close affinities between the 

 ambulacral field itself and the solid portion of the arms. The passage 

 directly beneath the field is probably the dorsal or axial canal, which by 

 the inverted position of the arms became the inner instead of the outer 

 passage. The hydrospires in the Blastoids are placed beneath the canal, 

 and extend along the perivisceral cavity of the body, like in the case ot 

 Teleiocrinus. 



