360 MARINE INVERTEBRATES 



long and slender, with short peduncles for the eyes ; the opercu- 

 lum is corneous, with a central nucleus. The animals are herbiv- 

 orous, feeding upon algae. The trochids are essentially tropical 

 shells, and the most of the genera which are comprised in the 

 family are only to be encountered in the warm waters of the 

 Pacific and Indian oceans. Some forms are very beautiful, and 

 frequently are used as mantel ornaments, and the shells of one 

 little species, which is opalescent in its coloring, are still exten- 

 sively gathered in the East Indies, to be polished and strung like 

 pearls in necklaces. 



GENUS Margarita 



On the Atlantic coast north of Cape Cod the trochids are rep- 

 resented by the genus Margarita, with five or six species. The 

 shells are small, thin, and globosely depressed, with smooth or 

 transversely striated whorls. The aperture is nearly circular, 

 with a simple lip. 



M. dnerecu This species has several prominent revolving ridges 

 upon the upper side of the whorls, with finer ones on the base. Very 

 fine growth-lines cover the entire shell. It ranges all along 

 the coast north of Cape Cod, but is not usually found between 

 tides. The writer has dredged many specimens in shallow 

 water at Eastport and Bar Harbor. 



M. Jieliclna. A thinner and more globose species than the 

 ! as ^' w ^^ a translucent, shining, smooth surface of a yellow- 

 ish or olive color. M. helicina is very fond of the leaves of 

 Laminaria, and is often found clinging to them when 

 storms have torn these great algaB from the bottom and ^\*~\ 

 cast them upon the shore. At Bar Harbor they are com- ARK^, i I i 

 mon upon the eel-grass in Rodicks Weir. This species can ^HP^) 1 

 generally be distinguished by its iridescent, metallic luster. 



D -mf i j , Marnantn licliciiiii. 



M. unaulata. A commoner species, perhaps, than 

 either of the preceding, sometimes found on the rocks of sheltered 

 coves at exceptionally low tides. Judging from the number 

 often to be found in the stomachs of fishes, they must be con- 

 sidered excellent food by the cod and its allied species which 

 thrive along the Maine coast. No doubt millions of M. undulata 

 are yearly destroyed in this way. The shell is depressed, 

 with four rounded whorls, a flattish base, and a large umbilical 

 opening. In color it varies from rose-red to brown. The surface is deco- 

 rated with numerous revolving raised lines placed at uniform distances. 

 Just below the suture the body-whorl is somewhat undulated with short 

 folds. Height three tenths of an inch, base four tenths of an inch. 



