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 Nudibranchidee, 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, as 
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 
ee ie ; of examination, but is too 
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 Dorts, 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 spicule. 
Of the family Dorida, the Polycera lessoni is a familiar form. It may be found on 
the alge 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 j S&S 
briefly described. In this family, DENDRONOTUS.—Dendronotus arborescens. 
called Tritonidee, the gills are ar- 
‘anged in lines along the sides of the back, and the tentacles can be withdrawn into their sheaths. 
The DENDRoNoTUS, 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 back. 

