TRTBE DIASPIDINI 307 



two lobes together never forming single com- 

 pact semicircular area. 



k. Pygidium with median pair of lobes nor- 

 mal in form, never minute and plate-like. 

 1. Pygidium with oraceratubae of breva- 

 ceratubae arranged in crescentic trans- 

 verse rows, sometimes few in number, 

 m. Pygidium with rows of oraceratubae 

 of brevaceratubae of each side of 

 meson divided into two prominent 

 subgroups. 



n. Pygidium with median pair of lobes 

 sometimes adjacent, but never fused, 

 o. Pygidium with three or four pairs 

 of lobes. 



p. Pygidium with four pairs of 



lobes. Type, Chionaspis lani- 



ger Newst.-Sclopetaspis MacG. 



pp. Pygidium with three pairs of 



lobes. Chionaspis Sign. 



oo. Pygidium with one or two pairs 

 of lobes. 



p. Pygidium with two pairs of 

 lobes. Type, Chionaspis gram- 



inis Green 



Duplachionaspis MacG. 



pp. Pygidium with one pair of 



lobes. Type, Chionaspis cole- 



mani Knw 



Unachionaspis MacG. 

 nn. Pygidium with median pair of lobes 

 fused on proximal portion, remain- 

 der of lobes divergent or adjacent, 

 rarely completely fused; combined 

 lobes not semicircular, 

 o. Pygidium with three pairs of lobes. 

 Type, Chionaspis americana 



Johns. Fundaspis MacG. 



oo. Pygidium with one pair of lobes. 

 Type, Diaspis chionaspiformis 



Newst. Africaspis MacG. 



mm. Pygidium with rows of oraceratubae 



of brevaceratubae few in number and 



not divided into two subgroups. 



n. Body with head and thorax together 



distinctly more than twice as long 



as abdomen. Type, Chionaspis 



elongata Green Greenaspis MacG. 



