340 



THE DENDRONOTUS. 



while the flat, white, pearly shell is perched horizontally on the very middle of the back, just 

 like an Eastern umbrella held over the palanquin of some great potentate. The color of the 

 animal is dull ochreous-yellow. 



WE now arrive at a very remarkable series of mollusks which have been separated by 

 systematic naturalists into a distinct section, appropriately called Nudibranchidse, or Naked - 

 gilled Mollusks, because their gills are always external and placed on the back or sides of the 

 animals. Many of these strange creatures are to be found on the European coasts ; and if the 



reader should wish to gain a 

 further insight into their 

 habits, and to examine the 

 marvellous forms which the 

 different genera assume, a& 

 well as their exquisitely deli- 

 cate and varied coloring, he 

 is referred to the magnificent 

 work of Messrs. Alder and 

 Hancock. The entire struct- 

 ure of the Nudibranchs is- 

 most curious and well worthy 

 of examination, but is too- 



s.-Dorfa puosa. 



purely anatomical for admis- 



sion into these pages. A few, however, of the more notable structures will be mentioned in 

 the course of our description. 



Our first example is the COMMON DORIS, a slug-like animal, which is represented in our 

 illustration in the act of swimming. The figure is much magnified. All the members of the 

 family to which this creature belongs may be known by the plume-like gills set in a circle on 

 the middle of the back, like the feathery coronet with which the Blackfoot Indian adorns 

 the head of his horse, and the two tentacles placed more towards the front. In the skin are 

 imbedded a vast number of little spicula?. 



Of the family Dorida, the Polycera lessoni is a familiar form. It may be found on 

 the algae in still pools left by the tide. 

 In the bath-houses at Cragie's Bridge, 

 in Boston, it is common. It is the 

 same as the European species. It is 

 a pleasing form, and proves an agree- 

 able addition to the aquarium. 



DORIS (Doris bilamellata). About 

 an inch in length. This is also a cos- 

 mopolitan form. It inhabits similar 

 localities as the former, at Beverly 

 and Nahant. Stimpson dredged it in 

 Boston harbor. Doris tenella, about 

 half the size, is found in same places. 

 Several other species are found on our 

 New England coast. 



THE next family is represented 

 by two species, each of which will be 

 briefly described. In this family, 

 called Tritonidse, the gills are ar- 

 ranged in lines along the sides of the back, and the tentacles can be withdrawn into their sheaths. 



The DENDRONOTITS, which is represented in the accompanying illustration, derives its very 

 appropriate name from two Greek words, the former signifying a tree, and the latter the bark. 



