NEREIS. 157 



The extremity of some specimens had been regenerated. 



PLATE XX. 



FIG. 19. Nereis contorta, enlarged. 



20. Section of the body, shewing the segments, pencils, and spine, more 

 enlarged. 



12. NEREIS MONOCEROS. The Unicorn Nereis. Plate XXII. 

 Figs. 9, 10, 11, 12, 13. 



Length eight lines or more ; breadth the third of a line. Body 

 nearly linear, subdivided into about seventy segments. A long antennu- 

 lar organ, somewhat of a moniliform appearance, issues from the centre of 

 the anterior extremity, and the posterior extremity terminates in a long 

 fork of two similar moniliform organs. Four red eyes, set in a quad- 

 rangle, occupy the upper surface of the head, from amidst which the 

 single antennular organ distinctly orginates. The site of a large probos- 

 cis is denoted by a white part near the anterior extremity. Three kinds 

 of appendages belong to each segment ; a longer pencil, consisting of a 

 larger pencil of several very transparent, delicate, bristly hairs ; also a 

 shorter pencil, together with a fleshy spinous prolongation. 

 This animal constructs a slight tube on the side of its vessel. 



It is rare. 



Perhaps it may prove allied to the genus Syllis, or be incorporated 

 with that race. 



PLATE XXII. 



FIG. 9. Nereis Monoceros, enlarged. 



10. Head, more enlarged. 



11. Posterior extremity, enlarged. 



1 2. Section of the body, enlarged. 



13. Segments, enlarged. 



