EXPLANATION OF PLATE A. 



Fig. I. Pelvis of Penlremites stilcatus. 



Fig. 2. Section of fork piece of P. sulcatus showing the ledges to which the poral pieces 



are attached. 

 Fig. 3. Transverse section of P. sulcatus just below the apex of the ambulacral field. 

 Fig. 4. External surface of deltoid piece. 



Fig. S a. Side view of deltoid piece showing the furrows in which the plicas rest. 

 Fig. S f>- Side view of deltoid piece showing (a) lateral expansion, {b) base portion of 



same. 

 Fig. 6. Transverse section of ambulacral field: (a) lancet piece, {b) poral pieces, (c) 



prongs of fork pieces, {d) zig-zag plicated integument. 

 Fig. 7. Surface view of the ambulacral field : (a) lancet piece, {b) poral pieces, (c) poral 



openings. 

 Fig. 8. Summit of P. sulcatus slightly ground to show connections of deltoid pieces, am- 

 bulacral field, and ovarian openings : {a) deltoid piece, (6) ambulacral field, 



(c) ovo-spiracle aperture. 

 Fig. 9. Oblique section of fork piece and ambulacral field : {a) fork piece, (&) hydro- 



spiric plicas, (c) ovi-duct, (d) canal beneath the lancet piece, {e) perforation 



of lancet piece, (/) poral pieces, (^) lancet piece, {h) plicated zig-zag inte- 



gument. 

 Fig. 10. Summit of P. sulcatus, not ground. 



Fig. II. Ventral surface of calyx, composed of pelvis and fork pieces. 

 Fig. 12. Dorsal surface of calyx, composed of lancet pieces and deltoid pieces. 

 Fig. 13. Diagram of a pentremite showing the relation of the pieces at the summit: (a) 



fork piece, {b) deltoid piece, (c) lancet piece, {e) poral piece. 

 Fig. 14. Interior view of fork piece and ambulacral field, showing the longitudinal furrow 



of the lancet piece. 

 Fig. 15. External view of zig-zag plicated integument. 

 Fig. 16. Interior vievsr of ambulacral field. 

 Fig. 17. Vertical section through the calyx of P. sulcatus showing the thickness of the 



plates. 



EXPLANATION OF PLATE [5. 



Fig. I. Pentremiies spiuosus. 



Fig. 2. Pentremites nodosus. 



Fig. 3. Pentremites ahbreviatus. 



Fig. 4. Pentremites Potieri. 



Fig. S- Pentremites clavatits. 



Fig. 6. Pentremites Broadheadi. 



Fig. 7. Pentremites hetnisphericus. 



Fig. 8. Pentremites Chestriensis. 



Fig. 9. Pentremites basilaris, 



Fig. 10. Pentremites sulcatus, showing cast of laterniformis. 



Fig. II. Pentremites 5?</<rn/«5— abnormal in having a longitudinal piece inserted between 

 two fork pieces. 



iv— 1— 160J 



