PLATE XVI I r. 



CoDASTER TRILOBATUS, var. ACUTUS, McCoy, vai - ., D. 269. 



I '. 



Fig. 1. Cross section of an ambulacrum, with the side plates in position, the lancet-canal 

 visible, and five hydrospire-tubes on each side. Carboniferous Limestone, 

 Lancashire. x 10 88 



Cryptoschisma Schulzi, d'Archiac is de Vern. } Bp., p. 281. 

 Pig. 2. A similar section, with eight hydrospire-tubes on each side. Lower Devonian, 



Asturias. x 9 '.)() 



Pentremites piriformis, Say, p. 167. 

 Fig. 3. A similar section, with the side plates in position and the lancet-canal visible; 

 seven hydrospire-tuhes on each side. Subcarboniferous, Illinois. Coll. Wachs- 

 muth. x8 l.s 



Pentremites elongatus, Shutnard, p. 161. 



Fig. 4. A similar section, three hydrospire-tubes on each side. Subcarboniferous, Iowa. 



Coll. Wachsmuth. x (5 Hi 



Pentremites sulcatus, Roemer, sp., p. 1G5. 



Fig. 5. A similar section, the side plates in position, with six hydrospires on one side and 

 four on the other. The concavity of the whole ambulacrum is well shown; 

 another figure of it is given on PI. XVI. fig. 20. Subcarboniferous, Illinois. 

 x4 41 



Pentremites conoideus, Hall, p. 162. 



Fig. 6. A similar section, four hydrospire-tubes visible on each side. Subcarboniferous, 



Indiana. x -4 46 



Fig. 7. Internal aspect of a radial plate with one of the limbs broken. Subcarbo- 

 niferous, Indiana. Coll. J. G. Hinde. x 2 95 



Fig. 8. Exterior of the same plate, after removal of the ambulacral plates and hydrospires, 

 -which last are cut oil' from the body-cavity by the ingrowth of the sides of the 

 sinus. x 2 !).". 



Orophocrinus gracilis, M. § W., sp. 



Fig. 9. Summit view (after Meek and ^Yorthen), showing the spiracular clefts. Subcar- 

 boniferous, Iowa. x ? 98 



Triccelocrinis obliquatus, Roemer, sp., p. 206. 



Fig. 10. External aspect of a broken radial plate, with the sinus and ambulacrum extending 



three fourths the length of the plate. Subcarboniferous, Indiana. Natural size. 95 



Fig. 11. Interior of the same, 'with no appearance of a sinus excavating the plate, and the 



hydrospires situated in the substance of the plate at its upper end. Natural size. !)."> 



Fig. 12. External aspect of another radial. Natural size 95 



