198 CATALOGUE OF THE BLASTOIDEA. 



radial limbs of this individual, which might be taken as indicating the presence of 

 the deltoids externally ; but we think that they are only clefts in the calcite, and 

 not radio-deltoid sutures. 



Distribution. If we are correct in referring to Metablastus the imperfect specimens 

 from the Niagara Group which have been described by Hall as Pentremites subcy- 

 lindrica and Cadaster pentahbus respectively, then the genus dates back to Silurian 

 times. Failing these, the oldest representatives of the genus would be M. Cottaldi, 

 Mun.-Chalm., sp., from the Lower Devonian (Taunusien) of France, and M. His- 

 panicus, E. & C, from a slightly higher horizon (Eifelien) in Spain. There is a 

 doubtful species in the Plymouth Limestone (Middle Devonian) of Britain ; but the 

 majority of the forms are from the American Carboniferous system. The type 

 species, 11. lineatus, occurs in the Upper Burlington Limestone, two are found in the 

 Keokuk Group, and two more in the Warsaw Limestone, though none are known in 

 the Kaskaskia Limestone, which contains Pentremites in such abundance. 



Species. The following list contains the names of the species which we refer to 

 Metablastus, together with one or two other doubtful types which appear to us to 

 be undoubted members of the Troostoblastidae, though their generic position is 

 uncertain : — 



Belocrinus Cottaldi, Munier-Chalmas (MS.). Gres de Gahard, Lower Devonian ; 



France. 

 Troostocrinus Hispanicus, E. & C. Calcaire d'Arnao, Lower Devonian ; Spain. 

 Pentremites lineatus, Shumard. Upper Burlington Limestone, Subcarboniferous ; 



Illinois and Iowa. 

 Pentremites Yarsouviensis, Worthen. Warsaw Limestone, Subcarboniferous; 



Illinois. 

 Troostocrinus Wachsmuthi, Gurley. Warsaw Limestone, Subcarboniferous; 



Indiana. 

 Pentremites Wortheni, Hall. Keokuk Limestone, Subcarboniferous; Iowa, 

 Illinois, Indiana. 



Doubtful Species. 

 Pentremites subcijlindrica, Hall & Whitfield. Niagara Group, Upper Silurian ; 



Ohio. 

 Codaster pentahbus, Hall. Niagara Group, Upper Silurian ; Indiana. 



The above list includes nearly all the species which we formerly referred to 

 Troostocrinus, of course with the exception of T. Iteinwardti and T. Grosvenori, to 

 which we now limit this name. But we now omit the Pentremites subtrimcatus of 

 Ball, which we formerly took to be a Troostocrinus, on account of his describing it 

 as belonging to the same type of form as P. UcinwnnUi, and we suspect that it will 

 turn out to be a Codaster. We also omit the Pentremites clavatus of Hambach, 



