300 



LO WER INVER TEBRA TES. 



In Tethys we have another peculiar form embracing some of the largest of the 

 naked molluscs, T. fimbriata, occasionally reaching a foot in length. Its general 



appearance can be seen from our illustra- 

 tion, which, however, fails to convey any 

 imjiression of the coloration of the animal. 

 It is nearly transparent, and covered with 

 dots and sjiots of red of different shades, 

 some so dark as to be almost black. The 

 curious gills on the upper surface were 

 once described as parasites. It is a native 

 of the Mediterranean, and, though often 

 captured, it lives but a short time in 

 aquaria, even in the large ones of the 

 Naples Zoological Station. It is a ra- 

 ])acious animal, feeding n])on other mol- 

 luscs and small crustaceans. 



In tlie remaining forms the branchiae 



are arranged ujion the back in a more or 



less complete circle which surrounds the 



anus. As an example of the Polycerid^ 



we may mention the beautiful Poh/cera 



lessonii of our coast, with a pale, tlesh- 



colored bodj', flecked with bright green, 



while the tentacles, gills, and tubercles on 



the back are variously spotted with white 



or yellow, and occasionally green. There 



^ are several other American forms in this 



family. 



The Phyllirhoid.£ is a very peculiar family, whose position among the molluscs 



would not be certain were it not for the fact that it possesses a lingual ribbon. 



Phyllirlioe hucephahis, the best known species, is a thin, compressed, translucent ani- 



FlG. bil.— Phyllirhoe bucephai. 



heart; i, intestine; /, lii 

 gland ; v, vent. 



reual organs; 5, salivary 



mal with a rounded, fin-like tail, which swims freely through the water in much the 

 same manner as a fish. The liead is furnished with two long tentacles, gills ai-e absent, 

 and the intestine terminates on the right side of the body. Most of the specimens 

 bear a jiarasitic medusa, Mtiestra parasitica. The most interesting fact connected 

 this animal is its jihosphorescence. At night, when swimming in the sea or in an 



