1881.] NATURAL SCIENCES OF PHILADELPHIA. 203 



frequently meet before reaching the peristome, but the anterior 

 ray is always distinctl}^ separated. 



Whenever tubular canals have been observed, they are pre- 

 served only to the border of the central space, but none of 

 them have been found to join in the centre. In a specimen of 

 Actinocr. glans, however, the tubes before terminating bend down- 

 ward toward the visceral cavity, give forth lateral processes, as if 

 disposed to branch, and expose two openings at the extremities 

 directed to opposite sides. The openings indicate that the tubes 

 ma}^ have been connected with each other by lateral passages, and 

 formed a ring around the centre. This is evidentl}^ the structure 

 of Actinocr. Verneuilianus^ in which a circular vessel is observed 

 beneath the centre at a short distance from the vault ; no ambu- 

 lacral tubes are attached to it, but there are small radial openings 

 with which they might have been connected. The lower portion 

 of the ring is composed of minute interlocking pieces, with five 

 additional openings interradially situated. This ring is com- 

 paratively large, enclosing within its circumference the contracted 

 upper part of the convoluted digestive organ, which is well 

 preserved in the specimen from which these facts were obtained. 



A tubular skeleton, as above described, has thus far been 

 observed only in the Actinocrinidae, but a tubular passage beneath 

 the vault, in connection with the arm grooves and oral centre, has 

 been traced in most groups of the Palffiocrinoids, and no doubt 

 existed also in the Blastoids. In Cyathocri7ius, and probabl}' in 

 the Cyathocrinidse generall}^ the tube is constructed of two series 

 of pieces overlying the oral plates, and these again are covered by 

 two similar series of plates, which form a part of the vault. In 

 Granatocrinus the tubes follow the pseudambulacra, being 

 covered by three series of small plates which must be considered 

 extensions of the vault (PI. XIX, fig. 3). 



It is now generally conceded that the tubular canals beneath 

 the vault contain the same organs which in modern crinoids are 

 exposed on the ventral disk, and like them embrace the food 

 passages, and certain other vessels in connection with the ambu- 

 lacral system. In this view of the case, it is reasonable to further 

 consider tliat the annular vessel, above described, served as a 

 water-vascular ring. 



The relations between the vault and the ventral covering of 

 recent Crinoids are not so close as has been sometimes supposed, 



