40 CALAMOCRINUS DIOMED.E. 



calyx interradials essentially similar to those of the Pal^ocrinoids." (Car- 

 penter, Chall. Eep. p. 39.) 



Ill the recent Calamocrinus the interradials do not begin by a single 

 plate, but with two or three resting upon the upper angle of the first 

 radials, which are truncated for their reception. These are followed by 

 several others, more or less irregularly arranged, and together with the 

 interradials and the two lower brachials form the immovable wall of a 

 large cup. Up to the present time, no recent Ciinoid except Calamo- 

 crinus presents this structure. 



The mode of arrangement of the embryonic interradial plates of Antedon, 

 •figured by Dr. W. B. Carpenter (Plate XXXllI. Figs. 7, A, B, Trans. R. S., 

 1866), is very similar to that of Apiocrinus, only the plates are less nu- 

 merous, and they are permanent in Calamocrinus as well as in Thauma- 

 tocrinus, as suggested by P. H. Carpenter. 



Schliiter and Meek speak of the upper series of the interradial plates 

 as corresponding to the pinnules of free arms. It is difficult to understand 

 this, as in Calamocrinus we have both the interradials and the large basal 

 pinnules; although, as Carpenter has shown, there are many recent Cri- 

 noids (Pentacrinus, Metacrinus) in which the basal joints of the large lower 

 pinnules are closely fitted together. 



Carpenter (Chall. Eep., p. 45) considers the vertical series of plates of 

 the anal side, resting upon a basal below and gradually diminishing in 

 size in such genera as Onychocrinus,* Taxocrinus, Reteocrinus, and Xeno- 

 crinus, as similar to the anal appendage of Thaumatocrinus, only differing 

 from it in forming a part of the body, " being bound in with the rays by 

 minute interradial plates which are not present in Thaumatocrinus." 



Ventral Surface. 



Seen from the actinal side, the five branches of the food groove of the 

 ventral surface of the disk (Plate VI. Fig. 1) radiate from the angles of 

 the orals. They are protected by the comparatively stout and prominent 

 lateral and covering pieces of that part of the ventral disk which, when 

 brought into contact, practically close the food groove. The food groove 

 is simple to the first branch leading to one of the lower pinnules. The 

 first right hand branch of the anterior food groove leads to the first 



* Meek and Worthen say the space between the arm-like plates and the vault is occupied by minute 

 pieces, and that these are all in direct continuation with the vault. 



