190 THE CANADIAN NATURALIST. [June 



thin calcareous integument, witli the mouth even with the surface, 

 the swimming appendages aborted, and the vent closed up, it 

 would resemble the cup of an Actinocrinus, fig. 9, a. The 

 lateral orifice would then be both mouth and vent, as it is, at 

 first (according to Prof. A. Agassiz, Seaside Studies, p. 125), 

 in the embryo of Asteracanthion BeryUnus, The ambulacral 

 canals oi Bipinnaria are the homologues, in a general way, of those 

 which are found beneath the vault of Actinocrinus, and extend 

 out into the grooves of the arms. If the ventral perisome of the 

 Crinoid were to be removed (the internal organs remaining undis- 

 turbed) the arrangement disclosed would be that represented in 

 fig. 9, — a convoluted plate in the centre with the canals radiating 

 from it. The most striking difi'erence is the absence of the 

 oesophageal ring. According to the organization of Actinocrinus 

 there could be no cesphagus at that point, and consequently there 

 is no ring. The convoluted plate represents the madreporic ap- 

 paratus. The sucking feet of the Star-fish, most probably, re- 

 present the respiratory tentacles that border the grooves of the 

 Crinoids, but modified into prehensile and locomotive organs. 

 Bipinnaria and Actinocrinus agree in having the mouth in one of 

 the interradial areas, and in the absence of an orifice through the 

 perisome at the ambulacral centre. These two characters are 

 enbryonic and transitory in the Star-fish, but they were perma- 

 nent in most paleozoic Crinoids. 



In Codonites steUiformis (^Pentremites stelliforniis Owen and 

 Shumard), figs. 10, 11, the ambulacral centre, c, is completely 

 closed. Five minute grooves radiate out to the extremities of 

 the five angles of the disc. These grooves are identical with 

 those of Pentremites and Nucleocrinus, and were occupied by the 

 ovarian tubes. The ambulacral canals of the true Crinoids and 

 of the Star-fishes are represented in a rudimentary condition, in 

 this species, by the hydrospires which open out to the surface 

 through the ten fissure-like spiraclea, s. The oro-anal orifice is 

 interradial. G. steUiformis in external form, the interradial posi- 

 tion of the mouth, and the closed ambulacral centre, resembles 

 Bipinnaria and Actinocrinus, but differs importantly in having 

 its respiratory organs arranged in ten separate tracts, all totally 

 disconnected from each other. It is a lower form than Actino- 

 crinus, which in its turn is lower than Bipinnaria, and yet all 

 three are constructed on the same general plun. 



G. SteUiformis, although much resembling a Pentremite, is a 



