Genera of the IN'oeth American Palaeozoic Bryozoa. 457 



It consists of four thin fasciculi (Plate A, h). They have their 

 origin in the tunic /endocyst) near the top of the cell, two in the 

 front and two in the back, and are inserted in the opposite sur- 

 face of the tentacular sheath. 



In the Ilippocrepian forms the muscles differ somewhat from 

 those just described, principally owing to the difference in the 

 structure of the tentacular crown. 



The presence of the epistome necessitates another muscle for 

 its movements. It arises from the tentacular disc, within the 

 cavity of the. epistome, and passing obliquely across the cavity is 

 inserted on the inner surface of the oval wall] of the epistome 

 (fig. 22, I). Its action is to elevate the epistome, raising it from 

 Ihe mouth. 



^~~ 



Fig. 24. Alcyonella flabellum, a, Endocyst ; b, Ectocyst ; /, CEsophagus ; g, Cardiac cavity of 

 stomach; p, Rotary muscles of tentacular crown; o, r, Radiating muscles; I, Polyp retractor 

 muscles (after Allman). 



The rotary muscles of the crown consist of two fascicles, which 

 take their origin at the same place as the retractor muscle of the 

 animal, and passing upward with that muscle,'^untir within some 

 58 



