MONOGRAPH OF THE EXISTING CRINOIDS. 509 



inch, that of the column alone being about 0.25 inch; when the arms are fully 

 expanded the diameter of their circle is about 0.5 inch. 



In Antedon biftda no anterior ciliated ring has been mentioned by Busch, 

 Thomson, or Carpenter. It is not unlikely, therefore, that it is absent in this 

 species. 



No observer has ever reported the presence of infrabasals, though Thomson's 

 examination was sufficiently thorough to enable him to detect the extremely minute 

 calcareous cylinders representing the first beginnings of the other calcareous plates. 



ANTEDON MOEOCCANA. 



Perrier's studies on the embryology and development of Antedon were based 

 upon larvae of Antedon moroccana sent to him by Prof. Camille Viguier from 

 Algiers, though he mentions, in passing, isolated observations on pentacrinoids of 

 Antedon bifida collected by himself at Roscoff. 



So far as can be seen from Perrier's description the development of Antedon 

 moroccana does not differ essentially from that of A. adriatica as given by Seeliger. 



Perrier appears to have been the first to notice that all the young of a given 

 mother are in the same developmental stage. 



The youngest fixed larva which he observed measured 0.21 mm. in length and 

 0.13 mm. in breadth. 



Perrier makes no mention of infrabasals, and it is quite possible that they are 

 absent from the young of this species, as well as from the young of the closely 

 related A. bifida, occurring only in the more primitive A. adriatica (five) and 

 A. mediterranea (three). 



COMACTINIA MEEIDIONALIS. 



In connection with Mr. Frank Springer's monograph on the Crinoidea Flexi- 

 bilia his assistant, Dr. Herrick E. Wilson, made a study of the development of 

 the digestive tube in the pentacrinoid larvse of Comactinia meridionalis. 



He found that in the early prebrachial stage the alimentary canal consists 

 of a mouth, surrounded by a narrow lip from which the oral tentacles spring; 

 a short, broad, funnel-shaped esophagus; a horizontal portion distended trans- 

 versely, resembling the human stomach, into the larger end of which the esophagus 

 opens; and a slender intestine ending blindly which originates at the smaller left 

 end of the stomach, makes a half turn, and coils dextrally around it. 



This simple alimentary system is loosely suspended in the ccelome by threads 

 and lamellae of connective tissue, and is in contact with the inner wall of the cup 

 only at the mouth and at the posterior end. 



The intestine in its development has coiled dextrally around the stomach, 

 then turned obliquely upward toward the posterior interray, the upward turning 

 having commenced near the middle of the anterior border of the right posterior 

 basal, and ending in this stage with the formation of the anus slightly to the right 

 of the posterior interradial plane, on a level with the distal margins of the 

 incipient radials. 



