Hambach — Revision of the Blastoideae. 35 



B. Order Irregulares. 



1. Family Olivanidae. 



1. Genus Olivanites. 



2. Family Eleutheroblastidae. 



1. Genus Eleutheroblastus. 



Blastoideae are dicyclical Pelmatozoa. The body is com- 

 posed of twenty pieces (at least in the embryonic state), 

 arranged in two circles of even numbers and an irregular 

 number of accessory pieces (say poral pieces), with the 

 exception of one order, Irregulares, where one or the other 

 circle contains an odd piece, a total difference from all others. 

 All were supported by a slender round or triangular column, 

 except one genus {Eleutherohlastus) as far as known. Geolog- 

 ically they belong to the Palaeozoic Age, commencing in the 

 upper Silurian, gradually increasing until they reach their 

 culmination point in the upper Subcarboniferous, and becom- 

 ing extinct with the close of the Chester limestone. Geo- 

 graphically they have been observed in Europe, Australia and 

 America, from which country the greatest number of species 

 has been described. 



Family Pentremidae. 



Body of various forms, all supported by a round or trian- 

 gular column. None of the summit openings permanently 

 closed except by the ambulacral integument. All of this 

 family, whenperfectly preserved, are known to possess pinnulae 

 and probably many of them, if not all, had a short proboscis. 



1. Genus Pentremites. 



General form of body globose, ovoid, conical, pyriform or 

 club shaped. Central orifice never closed except by the am- 

 bulacral integument, surrounded by eleven openings, which 

 appear externally as five, and are constructed by the junction 

 of deltoid and lancet pieces. Deltoid pieces variable, visible 



