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 muUiporus (text-fig. 20; Plate 56, fig. 4), Lepidesthes colletti (text-fig. 21; 

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





3[o 



2{^" 



1 (CD 



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 huiiiiiglotiensis (Meek andWoTthen). Lower Carboniferous. Adapted from Plate 33, fig. 1. Venlrally 

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



17. Lovenechinus sepHcs 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 te.xt-fig. 18. 



18. Loi'etiechinus 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 interambulacrum. 



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

 fifth plate reaches the interambulacrum. 



21. Lejddesthes collclti Wliite. Lower Carboniferous. Adapted from Plate 70, fig. 3. Every eighth plate reaches 

 the interambulacrum. 



