PLATE 64. 



Lepidechinus imbricatus Hall. Page 399 



Fig. 1. Same specimen as photograph, Plate 62, fig. 5. Holotype. X 2.7. Two columns of low plates in each ambula- 

 cra] area, imbricating strongly ventrally. Eight columns of plates in the interambulacral areas A and I, the plates 

 imbricating strongly dorsally and from the center laterally and over the ambulacra. There is a single plate in the 

 basicoronal row, two plate's in the second row, and thence increasing dorsally to the full number of plates and columns 

 at the mid-zone. In area C, the introduction of columns ventrally is clear, but only seven columns can be counted 

 in this area. Probably an eighth column would have appeared aborally in the part which is wanting. 



Perischodomus biserialis M'Coy. Page 401. 



Fig. 2. Same specimen as photograph, Plate 62, fig. 6. X l.S. Internal view of the ventral side. Ambulacral plates 

 are broad, imbricating (in this view) dorsally and from tin- center laterally and over the adradials. Interambulacral 

 plates imbricate ventrally and toward the center of the ana us it is an internal view. (Compare text-figs. 32-3S, 

 p. 75, for imbrication seen from the exterior and interior.) The primordial interambulacral plates are in the basi- 

 coronal row, there are two plates in the second row, three plates in the third row, four plates in the fourth row, and 

 five plates in the fifth row. In area G two interambulacral plates from the dorsal side are in place, seen from the 

 exterior, but flattened down on to the ventral part of the test (compare Plate 74, fig. 2). This figure is in part re- 

 stored as indicated by dotted lines (p. 404). (Compare text-fig. 30, p. 70.) 



Fig. 3. Same specimen as photograph, Plate 62, fig. 7. X 1.9. Ambulacra are narrow, the plates low, the interambulaera 

 near the mid-zone each with five columns of rounded plates which imbricate strongly dorsally and from the center 

 laterally and over the ambulacra. Two of the columns, 3 and 4, drop out, passing dorsally in each ana. An eccen- 

 tric primary tubercle is on each adradial plate; similar tubercles occur on some [dates of median interambulacral 

 columns as shown in the photograph, but they were overlooked in making the drawing (p. 404). 



Fig. 4. The same from an area near the mid-zone ■ 3.6. Some ambulacral plates are pinched off so that they do not 

 reach across the half-area. 



Fig. 5. The same. X 3.6. Ambulacral plates near the apical disc, all crossing the half-area, pore-pairs uniserial. 



Fig. 6. The same enlarged. Ambulacral plates near the mid-zone alternately moderately wedge-shaped, strongly beveled 

 under the adradials. 



Fig- 7. 8. Lower Carboniferous, Hook Head, County Wexford, Ireland. Sedgwick Museum Coll., Cambridge, England, 



(after Keeping, L876, Plate 3, figs. 1 and 4). Cotype. 



Fig. 7. X 0.9. Five columns of plates in each of the three most complete interambulacral areas, two areas are imperfect. 



There are eccentric primary tubercles on adradial plates and also on some of the plates of the median interambulacral 



columns. 

 Fig. 8. Apical disc and part of the corona 1.8, There are five genital plates and one small ocular in place. 



Genital plates have numerous pores. The apical disc is small proportionately to the diameter of the test. 



Eccentric primary tubercles arc shown on several interambulacral plates and the same with secondary tubercles on 



one plate (p. 403). 



Fig. t drawn from nature; tigs. 2-6 from my sketches by J. Henry Blake; lig-. 7 and s copied by W. M. Harrows. 



