THE AMBULACRUM OF THE CORONA. 



59 



echinus springeri (text-fig. 19; Plate 52, fig. 2), Perischocidaris (Plate 67, fig. 1); or still more 

 additional isolated plates may be introduced to make many series of pores in each half-ambula- 

 crum, Melonechinus multiporus (text-fig. 20; Plate 56, fig. 4), Ijepidesthes colletti (trxt-fiK. 21; 

 Plate 70, fig. 1), and Meekechinus (Plate 76, fig. 1). In the Centrechinoida the pores of the 



21 



TEXT-FIGS. 15-21. Ambulacra of Palaeozoic Echini showing development of pore series by a drawing-out process of 

 plate movement. 



15. Palaeechinus elegans M'Coy. Lower Carboniferous. Adapted from Plate 31, fig. 1. All plates reach the 

 interambulacrum . 



16. Maccoya burlingtonensis (Meek and Worthen). Lower Carboniferous. Adapted from Plate 33, fig. 1. Ventrally 

 all plates reach the interambulacrum; further up, only alternate plates. 



17. Lovenechinus septies sp. nov. Lower Carboniferous. Adapted from Plate 45, fig. 2. Ventrally all plates reach 

 the interambulacrum; further up, every alternate plate. At the mid-zone the plates are as in text-fig. 18. 



18. Lovenechinus missouriensis (Jackson). Lower Carboniferous. Adapted from Plate 42, fig. 2. Every second plate 

 reaches the interambulacrum. 



19. Melonechinus springeri sp. nov. Lower Carboniferous. Adapted from Plate 52, fig. 2 Every third plate reaches 

 the interambulaorum. 



20. Melonechinus multiporus (Norwood and Owen). Lower Carboniferous. Adapted from Plate 56, fig. 4. Every 

 fifth plate reaches the interambulacrum. 



21. Lepidesthes collelli White. Lower Carboniferous. Adapted from Plate 70, fig. 3. Every eighth plate reach 

 the interambulacrum. 



