228 



THE AMERICAN MONTHLY 



[Aug., 



7.— Family: DRUPPULIDA. Two shells. 



A. — MEDULLARY SHELL SINGLE. 



Two polar spines equal. Lithatractus. 



Two polar spines unequal. Druppatr actus. 



No polar spines. Prunocarpus. 



B. — MEDULLARY SHELL DOUBLE. 



Two polar spines equal. Stylatr actus. 



Two polar spines unequal. Xiphairactas. 



8.— Family: SPONGURIDA. Spongy shell. 



A. — NO INNER SHELL. 



No inner latticed medullary shell. Spongoprumtm. 



B. — INNER LATTICED MEDULLARY SHELL. 



No polar spines. Spongodruppa. 



Two ])olar spines. Spongatractus- 



C.-^MEDULLARY SHELL DOUBLE. 



No polar spines. Spongoliva. 



Two polar spines. Spongoxiphus. 



B. — Two Chaiuhers. 



9.— Family : ARTISCIDA. One shell. 

 No solid s])ines or hollow tubes on poles. Artiscus. 



10.— Family : CYPHINIDA. Two shells, or more. 

 No polar tubes or spines. Cypassis. 



Two polar tubes. Cannartidium. 



C. — Matty Chambers (four or more). 



11.— Family: PANARTIDA. Four chambers. 

 No polar spines or tubes. Panartus. 



12. — Family: ZYGARTIDA. Six chambers, ormore. 

 No polar tubes. Onimatocampe. 



III.— DISCOIDAL SHELLS. 



Here are 31 genera which are divided into two main sections 

 according to the number and character of the shells. 



A. — A?i outer lenticular latticed shell, an intracap- 

 sular medidlary shell, simple or double. 



13.— Family: PHACODISCIDA. Margin withoutchambered 

 girdles. 



