GASTROPODS. 



357 



and the blackish irregularly white-edged dorsal eye-spots. It is vividly phosphor- 

 escent in the dark, and the phosphorescence at once appears if the creature is in 

 any way disturbed. It is said to be 



lively in its movements, and capable of 

 swimming freely in any direction ; but 

 has neither jaws nor radula. Specimens 

 are sometimes captured 8 inches to a 

 foot in length. In the genus Tritonia 

 the branchiae are numerous, and arranged 

 in a row along the lateral margins of 

 the back. There is a large frontal veil 

 above the mouth as in Tethi/s, and the 

 retractile tentacles are branched at the 

 ends. The horny jaws are large, and 

 the radula well developed. T. Itombergi 

 is the largest of the British nudibranchs, 

 being sometimes 7 or 8 inches in length. 

 It varies in colour from dark purple- 

 brown to light brown, flesh-colour, and 

 yellowish white. Dendronotus arbor- 

 escens is one of the most beautiful of 

 the naked Mollusca, the accompanying 

 figure giving a good idea of the 

 branched character of the gills. It 

 will be noticed that they are arranged 

 along each side of the tapering body, 

 that the head-veil is also branched, and 



wit t vm 



Dendronotus arborescens (enlarged) 



Tethys gorilla. 



that the laminated 

 tentacles are retractile 

 within branched 

 sheaths. The back 

 is reddish or yellowish 

 brown, marbled with 

 darker brown, and 

 spotted with white. 

 The animal is about 2 

 inches in length, and 

 has both jaws and 

 radula. It is not 

 uncommon on most 

 parts of the British 

 coasts, from low-water 

 mark to deep water, 

 and it also ranges 

 northward to Green- 

 land. It is also re- 



