160 NEREIS. 



2. SPIO CELATA Plate XX. Fig. 21. 



Two very minute, long, slender, flexible tentacula, waving and 

 searching about on the surface of shells, are to be sometimes observed 

 issuing from the low orifice of a short dark tube. Nothing besides can 

 be discovered. But, on dislodging the diminutive tenant of this fragile 

 edifice, it proves an animal, whose body, consisting of eight or ten 

 segments of a flattened form, with a bristle on each side, does not exceed 

 a line in extent. Two cartilaginous active tentacula, surpassing the 

 length of the body, are seated on the head, and on its upper surface, four 

 jet black eyes, set as in the corners of a quadrangle. Colour of the ani- 

 mal reddish-brown. 



The formation of the posterior extremity could not be positively 

 ascertained. 



PLATE XX. 



FIG. 2L. Spio celata. 



The Nereis forms a numerous tribe of fierce, apparently rapacious, 

 active, and restless animals, all of singular and interesting conformation. 

 Their external characters have been minutely detailed by MM. Andouin 

 and Milne Edwards ; in i*ecent publications by Signer Delle Chiaje, and 

 more early by M. de Bosc, after a Treatise by Savigny, which I have 

 not had the fortune to see. But almost all the illustrations which I 

 have been able to examine relate to the detail of the external conforma- 

 tion of the various parts, with the view of settling the precise position 

 of various genera in the Systema. 



The principles thus employed appear rather intricate and difficult to 

 be practised, therefore, however meritorious the plan, it might be per- 

 haps very desirable that some simple, yet explicit, method should be 



