188 EEPORT ON THE NUDIBEANCHIATE 



instances of considerable peculiarities of structure in individuals of 

 the species. I showed that the edges of the tentacular sheaths 

 which are usually " entire-edged '^ may occasionally be somewhat 

 undulate in outline ; and one specimen exhibiting this character^ in 

 addition to a genei'al paleness of colour and the possession of only 

 four velar tentacles, was seen to bring us very close to Alder and 

 Hancock's species Tritonia lineata, one oi the distinguishing characters 

 of which is the possession of " undulating margins " to the tentacular 

 sheaths. Of this " species " only two specimens were (or have been, 

 so far as I am aware) obtained, under stones at Scarborough. Now, 

 the genera Tritonia and Lomanotus are nearly allied, and though 

 they have diverged in certain points of internal structure yet they 

 still retain a great similarity in the structure and form of the dorsum 

 generally and of the epipodial ridges and tentacular sheaths in 

 particular. The undulating ridges of Lomanotus are to be seen in 

 Tritonia Homhergii, although the papillae of the former have gi^own 

 into the branchial plumes of the latter, the larger plumes being 

 simply developments of the larger papillae on the inward undulations 

 in Lomanotus. Therefore having established variations from the 

 usual type of entire-edged tentacular sheaths in a species of Tritonia, 

 I would adduce this as an argument for the probability of variation in 

 the coi'responding structures in any given true species of Lomanotus. 



Alder founded his species marmoraiws because of the entii-e-edged 

 sheaths and the irregular character of the epipodial papillee (added 

 to some peculiarities of colour) in his specimen. He judged his 

 specimen flavidus to be specifically distinct because of its possession 

 of tuberculated sheaths and better differentiated papilla3 on the 

 epipodial ridges. So also in describing Thomson's specimens from 

 Weymouth, he concluded them to be types of a new species for which 

 he suggested the name fimhriata because of the filamentary character 

 of the processes on the edges of the tentacular sheaths and epipodial 

 expansions. Dr. Norman also founded the species Hancocki partly 

 because of the small size of the dorsal tentacles in his specimen from 

 Torbay, but considerably because the edges of the sheaths were pro- 

 duced into " leaflet-like points " and the papillae of the lateral ex- 

 pansions were of " flat triangular " form. Norman, however, adds 

 a valuable observation. He says significantly, " The papillae 



are capable of contraction and dilatation, and are constantly 

 changing their apparent dimensions while the animal is in motion." 

 Very probably the '' leaflet-like points " of the tentacular sheaths 

 possessed the same contractility of tissue, for the edges of the sheaths 

 and of the epipodial ridges generally possess the same characters. 



It is most instructive also to compare the sizes of the different 

 specimens of Lomanotus described. Norman's example was two and 



