464 Mr. C. Collingwood on Nudibranchiute Mollusca. 



crawling out of the water in which they are placed ; so that some 

 hours afterwards it is not unusual to find them literally " high 

 and dry" upon the edge of the vessel, and, of course, dead. 



Polijcera ocellata. — Of the genus Polycera we may reckon 

 two species, though by no means commonly met with. The 

 above, which, however, very closely resembles the next, is the 

 least rare, and has been not unfrequently taken on the Egremont 

 shore and elsewhere. I have not met with it during the last 

 twelve months. 



Polycera Lessonii. — All that can be said of this, is that our 

 excellent naturalist, my friend Mr. I. Byerley, has taken one in 

 the dredge, off the North Cheshire coast, outside the Mersey 

 mouth ; so that no doubt it exists near us. But although the 

 Mersey shores offer a rich feast for the naturalist, the dredging 

 is anything but satisfactory, and experience has only resulted in 

 laying aside the dredge to a great extent, and trusting to the 

 sea-boots. 



Ancula cristata. — A lovely species, which I am glad to say is 

 one of our common Nudibranchs, especially on the Egremont 

 shore. It is here found under stones, in company with other 

 species to be mentioned presently ; and the little light speck 

 ensconced in a crevice bears but a faint resemblance to the graceful 

 creature into which it expands when placed iu the water. No 

 figure can do justice to the beautiful frosted silvery appearance 

 of the branchial plumes, or the delicate transparent whiteness of 

 the body ; and as it is an active little animal and constantly iu 

 motion, its beauties are readily viewed even without the aid of a 

 glass. Placed in the aquarium, they have lived for some weeks, 

 marching freely about and traversing all parts of the tank. They 

 were numerous early in the last February at Egremont; but 

 they appear to congregate on small circumscribed patches of 

 stones, so that it is not always easy to hit upon the exact spot. 



Tritonia Hombergii. — A magnificent animal, and the largest 

 of our Nudibranchs ; but being a deep-sea species, the wonder 

 is not that it has only occurred once or twice, but that it has 

 been picked up at all upon the shore. Alder and Hancock 

 state that it is seldom obtained except by the dredge or trawl. 

 It has, however, been taken on the western shore of the Mersey, 

 near its mouth ; and I have myself picked it up on the shore of 

 Hilbre Island, in the Dee estuary. Its great size, its very com- 

 plex tentacles, and its numerous tree-like tufts arranged all along 

 the sides, conspire to render it a creature once seen not soon 

 forgotten. 



Tritonia plebeia, another deep-sea species, has been taken in 

 the dredge outside the Mersey mouth. 



Dendronotus arborescens, — This very remarkable and beautiful 



