ECHINODERMATA—BLASTOIDEA. 



479 



sides. Radial plates long and narrow, with limbs much shorter 

 than the bodies and deep and narrow sinuses. Deltoids five, small 

 and similar. Ambulacra short and narrow. Lancet plates con- 

 cealed by side plates. Spiracles ten sHts, the posterior pair sepa- 



FlG. 1788. Troostocrinus reinwardti, FiG. 1 789. Metablastus lineatus. Sum- 

 X 2, with ambulacrum much enlarged, mit view, X 4- (After Etheridge and 

 ( After Roemer. ) Carpenter. ) 



rate from the anus and nearer to the mouth. Agrees with Tri- 

 coelocrinus in the position of the two posterior spiracles. Mis- 

 sissippic. 



3. M. lineatus (Shumard). (Fig. 1789.) Mississippic. 

 Calyx long and spindle-shaped. Basals and radials long and 



slender. (Type of genus.) 



Burlington of Missouri, Illinois and Iowa. 



4. M. wortheni (Hall). Mississippic. 

 Differs from M. lineatus in its longer ambulacra and heavier 



basal cup. 



Keokuk of Indiana, Illinois, Iowa and Missouri. 



IV. Tricoelocrinus Meek and Worthen. 



Differs from Troostocrinus in its calyx which is broadest below 

 and has a short and wide base, with the three spaces corresponding 

 to the flattened sides of Troostocrinus deeply and broadly exca- 

 vated. Ambulacra longer than in Troostocrinus or Metablastus. 

 Mississippic. 



