PLATE 56. 

 Melonechinus stewartii (Safford). Page 371. 



Fig. 1. Same specimen as photograph, Plate 54, fig. 1. Drawn from a wax cast of the holotype which is an external mold. 

 X 3.5. Oculars and genitals are all in place, and in addition a number of polygonal periproctal plates are in place. 

 This is the only specimen known in the genus in which the periproctal plates are known (p. 363). 



Melonechinus multiporus (Norwood and Owen). Page 375. 



Figs. 2-13. St. Louis Group, Lower Carboniferous, St. Louis, Missouri. 



Fig. 2. After Jackson and Jaggar, 1896, Plate 2, fig. 3. Mus. Comp Zool. Coll., 3,003. X 1.2. A nearly perfect ventral 

 area. There are four columns of plates in three of the ambulacra; in each interambulacrum there are two plates 

 in the basicoronal row and three plates in the second row (p. 376). 



Fig. 3. After Jackson and Jaggar, 1896, Plate 2, fig. 4. Mus. Comp. Zool. Coll., 2,994. Development of an ambulacrum. 

 X 3.5. Ventrally there are four columns consisting of demi- and occluded plates, higher up scattered isolated plates 

 appear in the middle of each half-area, still higher there are three, then four irregular columns of plates in each half- 

 area (pp. 228, 376). 



Fig. 4. Vanderbilt Univ. Coll., 218. Ambulacrum at the mid-zone seen from the exterior. X 2.3. Ten irregular columns 

 of plates consisting of two columns of wide occluded plates, two columns of narrow demi-plates, and six irregular 

 columns of isolated plates. Pore-pairs lie in that portion of each plate nearest to the next adjacent interambula- 

 crum (p. 376). (Compare text-figs. 13, p. 54; 20, p. 59; also compare Plate 56, figs. 2, 3. 4, and 6 with text-fig. 237, 

 p. 231.) 



l'iit. 5. Mus. Comp. Zool. Coll., 3,164 (from R. T. J. Coll.). X 2.3. Ambulacrum at the mid-zone, seen from the interior 

 (compare fig. 4). The two median columns of occluded plates are narrower than on the exterior. In the lateral 

 columns of demi-plates those lying opposite the horizontal interambulacral sutures are fan-shaped, which they are 

 not on the exterior (compare Plate 43, figs. 3, 4). The ambulacra] pore-pairs of occluded plates lie near the outer 

 margin of each plate; in isolated plates the pore-pairs lie near the middle of each plate and in demi-plates they lie 

 toward the inner margin of each plate, instead of all toward the next adjacent interambulacrum, as they do in all 

 plates, when seen on the exterior (pp. 60, 376). 



Fig. 6. Mus. Comp. Zool. Coll., 3,158. (from R. T. J. Coll.). X 4.6. In ambulacrum J there are six columns of plates 

 as far ventrally as shown, higher up there are four columns, and next the ocular only two plates, representing two 

 columns, a primitive, character (compare text-fig. 237, p. 231). Other ambulacral areas are similar, but with a less 

 complete reduction dorsally. Young interambulacral plates are in contact with the oculars. Ocular plates are all 

 insert and adorally cover the ambulacra and laterally the interambulacra in part on either side. Genitals with 

 three pores each (pp. 376, 379, 381). (Compare text-fig. 163, p. 149.) 



Fig. 7. Princeton Univ. Coll., 1,464. X 1.7. Showing peristomal plates, the only specimen known in the genus or family 

 with this character preserved. In the ambulacrum of the peristome there are two plates in an area orally, these I 

 consider as representing the primordial ambulacral plates, as seen in areas J and D; passing aborally, the plates 

 increase to many low small irregular plates in each area on the periphery of the peristome. Interradially there are 

 three non-ambulacral plates in an area: one adorally, and two in a row aborally. The base of the corona is quite 

 perfect, with four plates in the basicoronal row of each ambulacral area and two plates in the basicoronal row of 

 each interambulacral area (p. 378). 



Fig. 8. The same restored, with teeth and pyramids (compare text-fig. 48, p. 80), (pp. S2, 85, 362, 378). 



Fig. 9. Mus. Comp. Zool. Coll., 3,165 (from R. T. J. Coll.). X 1.8. A pyramid, with its ventral portion and tooth 

 restored as indicated by dotted lines (pp. 363, 379). 



Fig. 10. F. Braun Coll. X 2. Pyramids in place with teeth (p. 379). 



Fig. 11. After Jackson and Jaggar, 1896, Plate 5, fig. 20. Mus. Comp. Zool. Coll., 3,005. X 0.9. Specimen with nine 

 columns of plates in two interambulacral areas, the extreme highest number known in the species. Interambulacral 

 plates rhombic dorsally and strung out so that succeeding plates of a given column are separated and not in serial 

 contact as seen in the upper part of figure (p. 377) . 



Fig. 12. Mus. Comp. Zool. Coll., 3,161. X 2.4. Ambulacral plates with tubercles and pore-pairs in peripodia (p. 376). 



Fig. 13. After Jackson and Jaggar, 1896, Plate 2, fig. 1 . Mus. Comp. Zool. Coll., 2,988. X about 5. Spines tapering. 

 Si mie of the spines show slight constrictions, but these are quite probably accidental, as two other specimens of 

 this species in the Museum of Comparative Zoology 2,996 and 3,079, with excellent, spines show no evidence of 

 such constrictions (p. 377). 



Figs. 2, 7, 8, and 11 drawn by J. H. Emerton; fig. 13 by A. M. Westergren; all others by J. Henry Blake. 



