SYSTEMATIC PAET. 161 



But while the armlets of the Silurian Botryocrinus bear no pinnules, those of 

 the Subcarboniferous Steganocrinus give off pinnules from the armlets. 



Bather's classification and theories respecting the evolution of the arms 

 are open to many criticisms, and are certainly not confirmed by a study of 

 the Carboniferous Fistulata. He cannot put together certain Poteriocrinidse 

 with the Dendrocrinidge, and others with the Decadocrinidae, nor place the 

 non-pinnulate Homocrinus and Parisocriniis in a family w^ith pinnule-bearing 

 forms. His classification is based principally upon two things : the presence 

 or absence of infrabasals, which he makes a subordinal character, and the 

 relations of the plates at the anal side among themselves and toward adjoin- 

 ing plates, upon which he separates the families. He was perhaps not aware 

 that in Barycrimis the radianal may be present or absent in the same species, 

 and that Parisocriniis would be substantially identical with Cyathocrinus but 

 for the presence of the radianal. As family characters he also relies upon 

 the mode of branching in the arms, and the structure of the tegmen, which 

 latter he has been able to observe in only a few genera. The remarkable 

 development of the posterior area into a ventral sac, which in 1890 was 

 regarded by him as an excellent ordinal character, is omitted altogether in 

 his present classification. 



While therefore we cannot agree with Mr. Bather upon his classification, 

 we fully acknowledge the excellence of his specific and generic descriptions 

 in his late work on the Swedish Inadunata, and the many fine observations 

 which he has brought out. His discoveries upon the orientation of the radials 

 in the Pisocrinidaa and Calceocrinidse are of the utmost value, and have 

 thrown new light upon these difficult groups. 



We regard as the best family distinctions among the Fistulata the 

 presence or absence of infrabasals, the presence or absence of pinnules, 

 and the relative size of the ventral sac. The structure of the tegmen, if we 

 knew more about it, might perhaps also afford good distinctions ; but the 

 modifications that occurred at the anal side of the cup, and the mode of 

 branching of the arms, can be utilized only for distinguishing genera. The 

 biserial arm structure did not obtain a foothold among the Inadunata until 

 near the close of the Subcarboniferous, and at no time became a constant 

 character. More important for generic separation is the mode of union 

 between the radials and brachials, and the form of the facet — whether 

 horse-shoe shaped or forming a straight line ; also the form of the ventral 

 sac, and whether one or more of the radials are compound. 



