PLATE 74. 

 Pholidocidaris irregularis (Meek and Worthen). Page 434. 



Fig. 1. Keokuk Group, Lower Carboniferous, Montgomery County, Indiana. F. Braun Coll. X 1.8. This specimen, 

 while imperfect and fragmentary, is most instructive. It represents a radial segment of a test flattened and distorted; 

 also part of the dorsal plates have been removed. As a result, we see the exterior of part of the plates of the dorsal 

 area (unshaded I and the interior of a portion of the ventral area (shaded for contrast); also a fragment of the lantern. 

 Ambulacral plates ventrally (shaded) are very large, about rhombic in form, with pore-pairs about in the middle of 

 each plate. On the other hand, ambulacral plates dorsally are small, and judging from the lower part of area B, 

 there are six columns in an area at the ambitus. The interambulacra are represented clearly only by dorsal plates, 

 column 1 of area A, column 2 of area C, and columns 2, 4, and 6 of area E (compare Plate 73, fig. 3). The adambula- 

 cral plates are striking, much larger than those of the median columns, scale-like, rounded, imbricating strongly; each 

 adambulacral plate bears a primary eccentric perforate tubercle, whereas there are no primary tubercles on the plates 

 of median columns. Two genital plates, g, have each numerous pores. A fragment of the lantern shows imperfect ly 

 a brace, b, two epiphyses, ep., and part of a pyramid, p (p. 439). 



Fig. 2. Keokuk Group, Lower Carboniferous, Keokuk, Iowa. F. Springer Coll., 8,015. X 0.9. This specimen, like the 

 last, is very fragmentary, showing part of the dorsal plates (not shaded), part of the ventral plates (shaded to differ- 

 entiate them), and an imperfectly preserved lantern. The specimen when alive was probably 100 mm. or more in 

 diameter. Ambulacral plates are confused and imperfect, the most obvious feature being that the dorsal plates 

 are small, as in fig. 1. The ventral (shaded) interambulacral plates imbricate toward the center of the area, and 

 adorally ; this is because they are seen from the interior. The dorsal plates (unshaded) clearly imbricate dorsally and 

 from the center outward (compare text-figs. 32-38, p. 75). Adambulacral plates bear each an eccentric perforate 

 primary tubercle and they are much larger than are the plates of median interambulacral columns. Six columns of 

 interambulacral plates can be made out with reasonable certainty in area E and with less clearness in other areas. 

 The lantern is strongly inclined, as indicated by the angles of the teeth (compare Plate 27, fig. 5); the pyramids, //, 

 are in place, also the teeth, (, and in three areas, D, F, and H, a small worn plate that is apparently the brace. 

 Below the letters D and F primary spines occur (p. 440). 



Figs. 3-7. Keokuk Limestone, Lower Carboniferous, near Burlington, Iowa. Univ. of Michigan Coll., 1,740, C. A. White, 



collector. X 1.8 (p. 438). 



Fig. 3. Adambulacral plate from column 1 (left side), showing an eccentric perforate primary tubercle with scrobicule 

 and secondary tubercles; the plate is rounded, scale-like in form, with lateral and ventral beveling and facets for 

 articulation with neighboring plates. 



Fig. 4. Adambulacral plate from column 2 (right side), otherwise similar to fig. 3. 



Fig. 5. Small adambulacral plate from column 1 (left side), similar to fig. 1; probably from near the mid-zone. 



Fig. 6. Right half-pyramid; showing a moderately deep foramen magnum and a suture for the epiphysis. 



Fig. 7. Left half -pyramid seen from within, showing pyramidal suture, dental slide, moderately deep foramen, and a wide 

 lateral wing. 



Pholidocidaris sp. Page 440. 



Figs. 8-10. Kaskaskia Group, Lower Carboniferous, Pulaski County, Kentucky. F. Springer Coll., 8,047. X 5.4. A 

 small species or a young individual, of interest only from its occurrence in the horizon and locality. 



Figs. 8, 9. Two ventral ambulacral plates; 8 seen from the exterior, and 9 from the interior. 

 Fig. 10. Genital plates, each with many pores. 



Pholidocidaris acuaria (Whidborne) Page 441. 



Fig. 11. Upper Devonian, East of Barnstaple, England (after Whidborne, 1898, Plate 25, fig. lb, the type of his genus 

 Protocidaris, here considered a synonym of Pholidocidaris). Museum of Practical Geology Coll., London, 7,158, 

 cotype. X 4.5. Interambulacral plates rounded, thin and scaly, with eccentric perforate primary and secondary 

 tubercles; primary and secondary spines in place. 



Pholidocidaris tenuis Tornquist. Page 440. 



Figs. 12, 13. Lower Carboniferous, Hunsrueken, Germany (after Tornquist, 1897, Plate 21, figs. 8 and 9, Plate 22, fig. 8). 



Cotypes. 



Fig. 12. Interambulacral plate. X 0.9; and enlarged X 5.4. With an eccentric perforate primary and secondary 



tubercles. 

 Fig. 13. Spine. X 1.4. 



Figs. 11-13 copied by W. M. Barrows; all others drawn by J, Henry Blake. 



