114 THS AMERICAN MONTHLY [Apr., 



SECTION B. CEPHALIS AND THORAX, 2 JOINTED 



SHELL. 



30.— Family: TRIPOCYRTIDA. Three radial apo- 

 physes. 



MOUTH OF THORAX OPEN. 

 Three radial ribs enclosed iu wall of thorax. No ce- 

 phalic wings. 



THREE THORACIC RIBS rROLONGKD INTO 3 TERMINAL FEET. 



Cephalis with horn. Dictyopliimus. 



THREE THORACIC RIBS PROLONGED INTO O LATERAL WINGS. 



Thorax latticed. Horn. Lithontelissa. 



Thorax latticed. No horn. Psilomelissa. 



Thorax with spongy frame work. Spojigojuelissa. 



Three radial beams free not enclosed in thorax. 

 Beams outside thorax. Eucecryphcdus. 



Three radial terminal feet on peristome. No ribs. 

 Feet solid. Lyvlinocaniuin. 



MOUTH OF THORAX CLOSED. 



Three divergent ribs enclosed in thorax. 

 Ribs in wall of thorax. Sethopera. 



Three divergent free lateral wings on sides of thorax. 

 Three solid lateral spines. Horn. Micromelissa. 



Three solid lateral spines. No horn. Peronielissa. 



Three terminal feet (on base of thorax). 

 Three feet solid. Tetrahedrina. 



Three feet latticed. Sethochytris. 



31.— Family: ANTHOCYRTIDA. Numerous radial 

 apophyses. 



Radial ribs smooth, (rarely thorny), enclosed in wall 

 of thorax. 



(Cephalis commonly small, without horns). 

 Shell ovate. Mouth constricted. JSethamphora. 



Shell pyramidal. Meshes simple. Setlwpyramis. 



Shell pyramidal. Meshes fenestrated. Plectopyramis. 



Radial ribs thorny, (rarely smooth} prolonged into free 

 terminal feet. 



