522 PROCEEDINGS OF THE ACADEMY OF [1899. 



epipodia is bright green and striated with numerous fine veins. The 

 epipodia are indented at their edges, and united behind in a very 

 ample dorsal expansion. On the back, a little behind the two 

 tentacles, is an elongated, bladder-like projection, containing the 

 heart, which pulsates regularly and rapidly. From this arise three 

 main trunk veins, each of which is numerously subdivided. This 

 arrangement seems to distinguish the animal from Elysia viridis, 

 and the coloration is unlike that of the other species described. 

 If it proves to be a distinct species, I would propose to call it 

 Elysia Hendersoni. Length, in alcohol, 17 mm. 

 Onchidium Tonganum Quoy and Gaimard. 

 Perorda tongana. 



This curious animal is very common on the Apia reef at low- 

 water mark. It is oval in shape, and attains a length of nearly 

 three inches. The mantle is of a dirty olive green, thick and cov- 

 ered with processes and warts, on some of which are eyes. The 

 tentacles are short, but the labial palps enormous. 



Though an ungainly looking creature, Onchidiuvi displays 

 greater activity and intelligence in its movements than any mollusk 

 except Cephalopods which I have seen. It may almost be said to 

 run, and if placed in a vessel at the bottom of a boat will make 

 a determined efiort to climb over the sides and reach the sea. As 

 it moves, the large posterior pulmonary orifice opens widely and 

 contracts. It must be capable of living under water, as it fre- 

 quents reefs which are submerged except at low tide, but in cap- 

 tivity, when placed in sea water, it invariably came out and wan- 

 dered on the balcony, but specimens placed under a heap of wet 

 seaweed remained quiet. It has been stated that Onchidium has 

 dorsal eyes only in those regions where Periophthalmus is found, 

 and that they assist it to escape the attacks of the fish. I cannot 

 support this statement from my own observation, for, though 

 Periophthalmus is common in Samoa, it frequents mud flats and 

 mangrove swamps, and I have never seen it on the edges of coral 

 reefa which are the habitat of Onchidium. 



It will be noticed that the majority of the Nudibranchs de- 

 sci-ibed belong to the Doridida; or Elysioidea, and that the yEolidce 

 and allied families are entirely absent. As Pease, who collected 

 chiefly in the Society and Hawaiian islands, also describes no 

 Solids, it looks as if the group was not numerous in the central 



