THECACERA. 



plates, seven in a row on each side, and can be distinguished from that of P. ocellata only by 

 the external plates, which are a little squarer and broader than in that species : the two 

 spiniferous plates next the median line are perfectly alike in both these forms, and the 

 tongue is divided down the centre by a naked space, in precisely the same manner. 



The nervous system has three pairs of oesophageal ganglia, arranged as in Polycera, only 

 the cerebroids are a little elongated in the antero-posterior direction, and the buccal ganglia 

 are closely united together. 



The nerves appear to be distributed as in that genus ; the eye is provided with a lens 

 and cornea, and is sessile on the cerebroid far forward on the outer border ; the auditory 

 capsules contain numerous otolithes, and seem to belong to the same ganglia. 



The skin is fine and smooth ; — the spicula have not been examined. 



