PLATE 42. 

 Lovenechinus missouriensis (Jackson). Page 337. 



Figs. 1-4. Burlington Group, Lower Carboniferous, Burlington, Iowa. F. Springer Coll., 8,126. An exceptional speci- 

 men for surface characters, as most specimens are internal or external silicified molds. Same specimen as photo- 

 graph, Plate 46, fig. 4 (p. 340). 



Fig. 1. A perfect ventral area to show developing stages. X 3.3. Ambulacral plates ventrally are primaries, and pore- 

 pairs are uniserial; a little higher up ambulacral plates are alternately primaries and occluded and pore-pairs are 

 biserial ; at the upper part of this figure the plates are demi- and occluded, and pore-pairs biserial, here having attained 

 the full generic character. In the interambulacrum there are two plates in the basicoronal row, three plates in the 

 second row, and four plates in the third row, as usual in this family (p. 340). 



Fig. 2. Ambulacrum near the mid-zone in area F. X 3.3. Demi-plates are all narrow, and occluded are wide; pore-pairs 

 lie near the interambulacral suture (p. 340). (Compare text-fig. 18, p. 59.) 



Fig. 3. Dorsal portion of ambulacrum D to show localized stages. X 3.3. In the lower part of the figure, ambulacral 

 plates are demi- and occluded, as is the typical character at the mid-zone. At the zone X, plates are primaries and 

 occluded, with pore-pairs biserial; passing dorsally, with some local irregularities, near the apical disc, at the zone 

 XX, the plates are all primaries and pore-pairs are uniserial, as are the plates built in the youth of the individual, fig. 

 1. (Compare text-fig. 237, p. 231.) At Y in each half-area occur a few isolated plates. Such have not been observed 

 in any other specimen of the genus, and as a progressive variation, are directly comparable to the typical character of 

 Oligoporus (p. 341). (Compare figs. 1-4 with text-fig. 237, p. 231.) 



Fig. 4. Ambulacral plates near the mid-zone enlarged for surface details. X 6.7. A relatively larger tubercle is on the 

 inner tongue-like end of each demi-plate (p. 340). 



Fig. 5. Same specimen as photograph, Plate 39, fig. 6. Internal mold. X 2.5. Ambulacral plates ventrally are all 

 primaries; higher up are demi- and occluded; plates opposite the interambulacral sutures are fan-shaped; the pore- 

 pairs are in the middle of the half-areas. Compare fig. 1 for internal and external characters at the same zone, also 

 Plate 43, figs. 1-5 (p. 346). 



Fig. 6. Same specimen as photograph, Plate 39, fig. 5, also Plate 41, fig. 1, dorsal area. X 2.5. In interambulacral 

 areas A, E, G, and I, column 5 drops out dorsally. In area I, the plates of columns 1 and 2 are developed to the 

 apical disc, but do not reach the surface, being roofed over by the lateral extension of the plates of columns 3 and 

 4 (seen diagrammatically in fig. 7). Oculars all reach the periproct and pores exist in oculars H and J (p. 89). 

 Genitals have three or four pores each. A few polygonal periproctal plates are in place, a very rare feature to be 

 preserved and the only case known in this genus (p. 343). 



Fig. 7. Diagrammatic section of areas H, I, and J, drawn in the line of the arrow in fig. 6. Ambulacral plates bevel over 

 the interambulacral plates of columns 1 and 2, which are occluded from the surface by the lateral extension of the 

 plate sof columns 3 and 4. The occluded plates marked X and *are the same plates as those that are similarly 

 marked in fig. 6. (Compare Plate 39, fig. 5.) 



