FAUNA OF THE CARBONIFEROUS AGE. 



395 



life. The gradual process of change may be clearly traced in the one, 

 but not yet in the other. Although Limuloids are clearly differen- 

 tiated first in the Carbon- 

 iferous, yet transition forms 

 may be traced even to the 

 Upper Silurian. If, with 

 Packard, we divide Crusta- 

 ceans into two groups — Pa- 

 laeo-carida and Neo-carida 

 (old style and new style 

 Crustaceans) — then Trilo- 

 bites, Eurypterids, and Lini- 



Fig. 546. 



Fig. 547. 



Figs. 545-548.— Carboniferous Lamellibranchs (after Meek): 545. Solenomya anodontoides. 

 546. Allorisma ventricosa. 547. Allorisma pleuropistha. 548. Astartella Newberryi. 



uloids, belong to the Palaso-carida. That these were all derived from 

 the Trilobite is shown by the transition forms 561 a and b, which must 



Fig. 549. 



Fig. 550. 



Fig. 552. 



Fig. 551. 



Figs. 549-552.— Carboniferous Gasteropods (after Meek): 549. Macrocheilns Newberryi 550 

 Pleurotomaria scitula. 551. Euomphalus subquadratus. 552. Bellerophon sublsevis (after Hall.) 



b 



Figs. 553, 554.- 



Fig 553. 



-Carboniferous Goniatites: 



Fig. 554. 

 553. Goniatites Lyoni (after Meek); a, side view; 



b, end view. 554. Goniatites crenistria (European); a, side view; 6, end view. 



