

IMBRICATION OF CORONAL PLATKS. 



7.-, 



TEXT-FIGS. 32-39. Method of imbrication of plates in Echini; the figures 32-38 an- NVIII lirtir, l>nw<l on Mudira o( 

 Lejndesthes colletti (Plates 69-71). 



32. External view, interambulacral plates are rounded in outline. Column 3 imbriratn* donially and laterally in two 

 directions. Columns 1, 2, 4 imbricate dorsally and laterally in one direction and over amhularrala. Ambulacra! platn 

 imbricate ventrally, bevel under adjacent interambulacrals, but do not otherwise have lateral tx'vrlinjj. 



33. Cross section of the same. 



34. Internal view of the same. Interambulacral plates are hexagonal in outline, angle* of inil>rir:iii<>n n-vrrwd from 

 external view, ambulacral plates with pores in the middle of plates, instead of near the interaiiiluilarnirn an in external view. 



35. Cross section of same. 



36. Optical section of plates seen from exterior. 



37. Optical section of plates seen from interior. 



38. Showing in vertical section direction of imbrication of plates in the inlet-ambulacrum and ambulacrum. 



39. Eucidaris Iribuloides (Lamarck). Bahamas. R. T. J. Coll., 693. X 4. Base of corona and peristome. On the 

 peristome both ambulacral and non-ambulacral plates imbricate adorally, a condition not known in the corona of any 

 echinoid. 



