Hambach — Revision of the Blastoideae. 43 



erally, sunk into the fork piece sinus so that the surface does 

 not touch the upper margin of the fork piece sinus. Lower 

 part of the body shows three distinctly depressed areas ; the 

 amount of depression varies in the different species. Inter- 

 am bulacral surface smooth or very finely striated. Summit 

 opening never closed except by the ambulacral integument. 

 Genital openings ten, of a slit-like appearance, on account of 

 the orifice opening obliquely. Anal opening so far below the 

 genitals that in large specimens it is almost i inch below the 

 summit, and as far as known not covered. All specimens 

 which I have had an opportunity to examine (over six hun- 

 dred) did not show any sign of a covering. Column triangu- 

 lar. This genus comprises Troostocrinus , Tricoelocrinus and 

 Meiablastus, and to show the gradual transformation from one 

 to the other I have given good figures of all our American 

 species on Plate IV. All described specimens are from the 

 Warsaw limestone or below from the lower Subcarboniferous 

 rocks. 



1. Saccoblastus bipyramidalis, Hall. Warsaw limestone. 

 Pentremites bipyramidalis Hall. 



Troostocrinus bipyramidalis Hall. 



Metablastus bipyramidalis, R. Etheridge fll. and P. H. Carpenter. 



2. Saccoblastus lineatds, B. F. Shumard. Burlington 



limestone. 

 Pentremites lineatus, Shumard. 

 Troostocrinus lineatus, Shumard. 

 Metablastus lineatus, Etheridge fll. and Carpenter. 



3. Saccoblastus obliquatus, Roemer. Warsaw limestone. 



Pentatrematites obliquatus, Roemer. 



Pentremites occidentalism Shumard. 



Tricoelocrinus obliquatus, R, Etheridge fll. and Carpenter. 



Troostocrinus laterniformis, Shumard. 



4. Saccoblastus woodmani, Meek and Worthen. Warsaw 



and Keokuk limestone. 

 Tricoelocrinus woodmani, Meek and Worthen. 

 Troostocrinus tooodmani, Meek and Worthen. 



5. Saccoblastus wortheni, I. Hall. Warsaw limestone and 



Keokuk. 

 Metablastus wortheni, R. Etheridge fll. and Carpenter. 



