312 



The body of N. umbilicatus is larger and more elongated than 

 that of N. Pompilius as it occurs in the South Seas, although the 

 specimens of the latter species brought from the Chinese Seas much 

 exceed both in size. In the N. umbilicatus, the longitudinal lamellae 

 on the median lobe of the external labial processes are divided by a 

 wide groove into two lateral sets, and the corresponding lamellae be- 

 tween the internal labial processes are about seventeen in number 

 and of considerable thickness. In N. Pompilius, the latter lamellae are 

 much thinner and more numerous, and the lateral sets of the former 

 are united together in the median line, commencing anteriorly with 

 an azygos transverse lamina. In both kinds, however, the corre- 

 sponding tentacula may be distinctly traced out, with only such 

 minor differences as might be expected to occur in different speci- 

 mens of either separately ; the digital, labial and ocular groups 

 agreeing sufficiently both as to number and character in the two 

 cases, considering the liability of these parts to slight modifications, 

 from arrest of development or redundance, in the same species. 



Referring to former observations of his own on the eye of N. Pom- 

 pilius, the author observes that they closely apply to N. umbilicatus, 

 which affords confirmation of his opinion that the pigmentary coat- 

 ing is subjacent to the retina. He finds no vestige of a lens, and in 

 place of vitreous humour, a mere viscous matter protecting the 

 retina from the sea-water. 



The organ of hearing, which had escaped detection in the speci- 

 men of N. Pompilius dissected by Professor Owen, altered as it 

 doubtless had been by long immersion in spirit, was discovered in 

 the example of N. umbilicatus examined by the author. It consists 

 of two spheroidal acoustic capsules placed, one on each side, at the 

 union of the supra and suboesophageal ganglia, and measuring about 

 one-twelfth of an inch in diameter. Each capsule rests internally 

 against the nervous mass, and is received on its outer side into a 

 little depression in the cephalic cartilage. It is enveloped in a kind 

 of fibrous tissue and filled with a cretaceous pulp consisting of mi- 

 nute, elliptical, otoconial particles, presenting under a high power a 

 bright point near each end, varying much in size, and sometimes 

 combined into stellate, cruciform or other figures. Cilia were not 

 observed within the capsules. 



The inside of the mouth is furnished with three groups of papillae, 



