168 ON SYSTEMATIC ZOOLOGY. 
Mytilus. Teeth none; hinge with a pointed depression. 
Shell fixed by a byssus. 
-Pinna. Teeth none; valves united at one end, open at the 
other. 
*** Univalves, spire regular. 
Argonauta. Shell with one cell; spire involute. 
Nautilus. Shell with many cells, communicating with each 
other by a. siphon. 
Conus. Aperture effuse, longitudinal, without teeth. 
Cyprea. Aperture effuse, linear, longitudinal, toothed each 
side. 
Bulla. Aperture a little contracted, and placed obliquely. 
Voluta. Aperture effuse; the pillar plaited. 
Buccinum. Aperture with a small canal leaning to the right. 
Strombus. Aperture with a small canal leaning to the left. , 
Murex. Aperture with a small straight canal. 
Trochus. Aperture contracted, and somewhat square. 
Turbo. Aperture contracted and orbicular. 
Helix. Aperture contracted, lunate on the inner side. 
Nerita. Aperture contracted, and semi-orbicular. 
Haliotis. Shell with a row of orifices along the surface. 
**EX Univalve shells, but without a spire. 
Patella. Shell conic, the aperture widening like a bason. 
Dentalium. Shell slender, subulate, open at both ends. 
Serpula. Shell tubular, mostly serpentine, adhering to other 
bodies. 
Teredo. Shell thin, pierced into wood. 
Sabella. Shell composed of agglutinated grains of sand. 
IV. Zooruyta. 
* With a hard calcareous stem. 
Tubipora. Animal inhabiting a coral, with cylindrical tubes. 
Madrepora. Animal inhabiting a coral with concave stars. 
Millepora. Animal inhabiting a coral with subulate pores. 
Cellipora. Animal inhabiting a coral, with hollow round 
cells. 
** With a softer stem. 
Gorgonia. Fixed. Stem horny. 
Alcyonium. Fixed. Stem corky. 
Spongia. Fixed. Stem stringy, flexile, absorbent. 
Flustra. Fixed. Stem covered with minute cellular pores, 
Tubularia. Fixed. Stem tubular, filiform. 
