CRINOIDEA. 



147 



No. 453. Platycrinus planus, O. & S. 



Basal plates. Burlington Limestone, Burlington, Iowa. 



No. 454. Platycrinus. 



Joints. In most Palaezoic crinoids the column, composed of joints, was 

 round, but in this genus it is oval or elliptical. The articulating facets are 

 marked striae radiating from near the center, which is characteristic of the 

 Palaeozoic forms. Sub-Carboniferous, Barren Co., Ky. 



No. 455. Crinoid. 



Stems. Burlington Limestone, Burlington, Iowa. 



No. 456. Crinoid. 



Roots. Sub-Carboniferous, Barren Co. ,-Ky, 



No. 457. Crinoid. 



Enlarged Joints. Sub-Carboniferous, Barren Co., Ky. 



ORDER BLASTOIDEA. 



The Blastoids connect tlie Cystideans with the true Crinoids. 

 They liave no arms, a short stalk, and the closed calyx resembles 

 a llower-bud. Five areas radiate from the summit, and carry 

 jointed pinnulae. This order began in the Upper Silurian, after 

 the Cystideans had declined. They culminated in the early Car- 

 Ijoniferous and disappeared in that age. Pentremites is the 

 characteristic genus. 



No. 458. G-ranatocrinus Norwoodi, O. & S. 



Burlington Limestone, Burlington, Iowa. 



No. 459. Neucleocrinus Verneuli, Troost. 

 Devonian, Columbus, Ohio. 



No. 460. Pentremites cervinus, Hall. 



This large form is from the Chester Limestone (Sub-Carboniferous), at 

 Chester, Illinois. 



No. 461. Pentremites Godonii, Defr. 

 Sub-Carboniferous, Huntsville, Alabama. 



No. 462. Pentremites pyriformis, Say. 

 Sub-Carboniferous, Cumberland Co., Tenn. 



