306 THE AMERICAN MONTHLY [Nov., 



Rings connected by 4 columns. Microcubus. 



Rings connected by 6 columns. Tympaniscus. 



Rings connected by S columns. Tympanidium. 



B.— WITH COMPLETE LATTICE SHELL. 



This division is huge compared to the former, containing 109 

 genera as against 11. But they fall conveniently into three sub- 

 orders distinguished by the character of the Cephalis. 

 V. ^pyroidea. — Cephalis bilocular. 

 VI. Botryodea. — Cephalis multilocular. 

 VII. Cyrtoidea. — Cephalis simple. 



V. — Cephalis bilocular. 

 21.— Family: ZYGOSPYRIDA. No thorax or second joint. 



A. — TWO BASAL FEET. 



Feet simple. Horn on apex. Dipnspyris. 



Feet simple. No horn on apex. Brachiospyris. 



Feet branched. Horn on apex. Dendrospyris. 



B. — THREE BASAL FEET. 



One horn on apex. Triposphyris. 



Three horns on apex. ■ Triceraspyris. 



No horn on apex. Tristylospyris. 



C. — FOUR FEET : TWO SAGITTAL AND TWO LATERAL. 



Horn on apex. Tetraspyris. 



D. — FOUR PAIRED LATERAL FEET, ONE APICAL, TWO FRONTAL. 



Three horns. Elaphnspyris. 



Two lateral or frontal horns on apex. Tanrospyris. 



No horn on apex. Therospyris. 



E. — FIVE BASAL FEET. 



One horn on apex. Clathrospyris. 



Three horns on apex. Aegospyris. 



F. — SIX BASAL FEET. 



One horn on apex. Hexaspyris. 



Three horns on apex. Liriospyris. 



No horn on apex. Cantharospyris. 



G. — SEVEN TO TWELVE OR MORE BASAL FEET. 



One horn on apex. Petalospyris. 



Three horns on apex (one apical, two frontal.) Anthospyris. 



Numerous horns on apex. Ceratospyris. 



No horn on apex, Gorgospyris. 



