LOVENECHINUS. 345 



4). The internal mold has impressions of the proximal faces of the plates, ridges representing 

 bounding lines, and siliceous filaments which are casts of ambulacral pores. The external 

 mold has impressions of the outer or distal faces of plates with tubercles, ridges representing 

 bounding lines of plates, and siliceous filaments which are casts of ambulacral pores as in the 

 inner mold. By studying the internal mold, and wax impressions made from the external 

 mold, it is possible to compare the external and internal characters of the same plates as if seen 

 in optical section (Plate 43, figs. 1-4). The ambulacrum seen from the exterior at the mid- 

 zone (Plate 43, fig. 3) has four columns of plates, wide occluded and narrower demi-plates, with 

 pore-pairs biserial and situated in the outer end of each plate, near the marginal suture. Two 

 rows of tubercles are on the occluded, and a single tubercle on the inner tongue of the demi- 

 plates. On the proximal or inner side of the very same plates (Plate 43, fig. 4), the occluded 

 and demi-plates are of about equal width. Demi-plates opposite horizontal interambulacral 

 sutures are higher and fan-shaped, and pore-pairs lie near the middle of the half-area. This 

 passage of pore-pairs from the middle to the outer margin of the area, in traversing the thick- 

 ness of the plates, is shown graphically in a unique bit of preservation (Plate 43, fig. 5), in 

 which we find proximally a mold of the interior, distally a mold of the exterior, and the pores 

 represented by slender siliceous filaments which traverse the hollow space originally occupied 

 by the plates. It is here seen that the filaments are strongly inclined laterally, being near the 

 middle of the area proximally, but close to the outer margin of each plate distally. Ventrally, in 

 the basicoronal row, as seen from the exterior (Plate 43, fig. 1), the ambulacral plates are all 

 primaries, and pore-pairs uniserial, lying close to the marginal sutures. On the interior at the 

 same zone (Plate 43, fig. 2) the ambulacral plates are also primaries, but the pore-pairs are 

 about in the middle of the half-areas. Passing dorsally, on the exterior at the zone marked X 

 (Plate 43, fig. 1), the plates are alternately primaries, expanded marginally, with those between 

 narrowed and nearly or quite occluded, pore-pairs biserial, as in Maccoya. On the interior 

 at the same zone marked X in Plate 43, fig. 2, the plates are still all primary, with pore-pairs 

 uniserial, again like Maccoya, but as seen from the interior (Plate 33, figs. 8, 9). Again passing 

 dorsally, on the exterior at the zone marked XX (Plate 43, fig. 1) the plates are demi- and oc- 

 cluded, the genus character. On the interior at the same zone, marked XX (Plate 43, fig. 2), 

 the plates are primary and occluded. They have therefore not yet taken on the character as 

 seen on the exterior, but have lagged behind in development, and are like the more ventral 

 plates of the exterior, and again like the typical plates on the exterior of Maccoya. This 

 close comparison that can be drawn by stages in development, as seen in plates ventrally, built 

 in youth, and the greater primitiveness of plates on the proximal side as compared with the 

 distal side, with the simpler characters of lower genera in the family, is all in favor of the re- 

 capitulation theory in evolution. Abundant similar cases are found throughout the Echini, 

 supporting the same view in the strongest way. 



