18 MR. C. TATE REGAN ON THE 



form a median groove, wliicli extends to the anal fin, decreasing 

 in size backwards (text-fig. 15 B) ; there is no efterent groove. 



The urinary opening (u.) is immediately behind the anus (a.). 



The genital opening is ventral and posterior, behind the 

 articulation of the ctenactinium (ct.). 



The ctenactinium is short and nearly straight, with denticu- 

 lated upper edge ; its articulation is ventral, and it lies on the 

 aproctal side of the priapium. 



Anteriorly the attachment of the priapium to the isthmus ends 

 at the level of the posterior edge of the eye ; in front of this is a 

 free terminal portion that ends in a second movable bony ap- 

 pendage, toxactinium (t.v.); this is rounded in cross-section, tapers 

 forwards, and curves towards the aproctal side, ending below the 

 extremity of the lower jaw. 



The pulvinulus (pv.) appears to be represented by a rounded 

 shield, with thick edges, that covers the basal part of the tox- 

 actinium below and on the aproctal side. 



b. Skeleton (PI. I. A). 



Third vertebra and first pair of ribs. — The transverse processes 

 of the third vertebra are normal and symmetrica], but bear no 

 ribs. The first pair of ribs are nearly symmetrical, but they are 

 not articulated with the vertebral column ; proximally they end 

 at the level of the second vertebra, but at some distance from it 

 on each side ; the proximal part of the rib of the proctal side 

 curves forwards to give attachment to the pleuro-priapial muscle. 

 These ribs run downwards and forwards, meet belo^v the peri- 

 cardium, and enter the priapium, where they run downwards and 

 towards the proctal side in front of the intestine. 



Cleithra. — Both cleithra are prolonged forwards and enter the 

 priapium, ending between the pulvinulus and the basal part of 

 the toxactinium (PL III. B, cl., cl.'). 



Priapial skeleton. — The axial bone (text-fig. 15, a.) is com- 

 paratively simple ; the toxactinium articulates with its anterior 

 end superiorly and proctally (PI. III. B, tx., a.), the ctenactinium 

 (text-fig. 15, ct.) with its posterior end inferiorly and aproctally. 



The antepleural cartilage of Neostethus is represented by an 

 antepleural bone that embraces the distal ends of the priapial 

 ribs and runs forwards on the proctal side of the axial bone, 

 ending a short distance behind the base of the toxactinium. 



The pulvinulus has no pulvinular appendage and no bones ; it is 

 a, ring of parenchymatous cartilage, but seems to have the structvu^e 

 of true hyaline cartilage in the middle (PI. III. B, pa.., pc). 



There are no infrasulcar bones, but the terminal part of the 

 vas deferens appears to be sup^Dorted by a bony lamina, as in 

 JVeostethus. 



c. Muscles. 



The muscles correspond to those of Neostethus, except that 

 (1) the pleuro-priapial muscle is attached proximally to the 



