116 CLASS IX. ORDER IV. 



out teeth, the valves united into one. 

 yielding byssus of which silk is sometimes made, 



ORDER 4, UNIVALVA. 



Soft animals, having shells with single valves. 



ARGONAUTA, (paper nautilus,) animal a sepia 

 or clio ; shell univalve, spiral, involute, membra- 

 naceous, one-celled. 



NAUTILUS, (pearl nautilus,) animal sepia ; 

 shell univalve, divided into several departments 

 communicating with each other by an aperture or 

 siphunculus. 



CONUS, (cone,) animal limax ; shell univalve, 

 convolute, turbinate ; aperture effuse, longitudi- 

 nal, linear, without teeth, entire at the base ; pil- 

 lar smooth. 



GYPRAEA, (gourie, sea-porcelain,) animal a li- 

 max ; shell univalve, involute, subovate, smooth, 

 obtuse at each end ; aperture effuse at each end, 

 linear, extending the whole length of the shell, 

 and toothed each side. 



BULLA, (dipper-shell,) animal a limax; shell 

 univalve, convolute, unarmed with teeth ; aper- 

 ture a little straitened, oblong, longitudinal, very 

 entire at the base; pillar-lip oblique, smooth. 



VOLUTA, (mitre, volute,) animal limax ; shell 

 one-celled spiral; aperture without a beak, and 

 somewhat effuse ; pillar twisted or plaited, gene- 

 rally without lips or perforations. 



BUCCINUM, (whelk, helmet-shell,) animal li- 

 max ; shell univalve, spiral, gibbose ; aperture 

 ovate, terminating in a short canal leanin i to the 

 right, with a retuse beak or projection ; 

 expanded, , 



