EIPLANATION OF PLATES. 



PLATE 36.— Continued. PA«K 



FIG. 19 — Summit view of a specimen having only four ambulacra, but 

 five radial plates. 



FIG. 20 — Side view of a deformed specimen. 



FIG. 21 — Summit view of a specimen with a ridge extending from the 

 distal end of an ambulacrum to the middle, along the lancet piece. 



FIG. 22 — Basal view of a specimen with si? radial plates and five am- 

 bulacra, but symmetrical as to base and summit. 



FIGS. 23-24 — Side and summit views of two internal casts. 



FIG . 2.5 — A side view showing the visceral cast where the test has been 

 removed. 



FIG. 26 — Interior view of two hydrospire groups in a broken specimen. 



FIG. 27 — Side view of a specimen showing the pinules along one am- 

 bulacrum. 



FIGS. 28-29 — End views of two ground specimens, showing hydro- 

 spires, pores, etc. 



FIG. 30 — A group of hydrospires magnified. See lancet plate and canal. 



FIGS. 31-32 — Side and ventral views of a specimen whose summit is 

 covered by a pyramid. 



FIGS. 33,34-35 — Side views of a specimen displaying two ventral 

 coverings, the outer so broken as to show galleries and tunnels. 



FIG . 36 — Side view of a specimen with a ventral pyramid. 



FIGS. 37-38 — Side and summit views of a four-sided specimen in 

 which one ambulacrum is traversed its full length by a ridge, fol- 

 lowing the line of the groove. 



PENTREMITES CALYCINUS, Lyon, Rowley. 125 



FIGS . 39-40 — Side views of two specimens of different sizes. 



PENTREMITES CONOIDEUS, Hall, Rowley. 126 



FIG. 41 — Side view of an elongate, ''four-sided" specimen, the non- 



ambulacral-bearing radial being turned toward the observer. 

 FIG. 42 — Ventral view of another "four-sided" specimen. 

 FIG. 4.3 — Side view of a deformed specimen. 

 FIG . 44 — Side view of a small specimen, preserving several stem joints. 



