Springer — Mysticocrinus. 667 



Infrabasals forming a shallow saucer, externally con- 

 cave; the two larger (compound) plates less than twice 

 the size of the smaller right posterior plate, which is cor- 

 respondingly enlarged; sutures meeting anterior, right 

 anterior, and left anterior basals. Basals strongly con- 

 vex, bent outwards and upwards, forming about one third 

 the height of the cup; posterior basal hexagonal, wider 

 than high, subangular below, truncate above; postero- 

 laterals pentagonal, narrower than posterior, and antero- 

 laterals still narrower. 



Radianal pentagonal, truncate above and beveling the 

 right lower corner of anal ; about one half as high as the 

 succeeding radial. Anal plate very large, sagittseform, 

 higher than wide, beveled laterally by the radianal ; apex 

 acuminate, rising almost to height of first secundibrachs ; 

 offsets of arrow head resting upon and interlocking with 

 distal margins of posterior radials. 



Radials unequal and differing in shape; angular pro- 

 cesses project nearly as high as the anal between the 

 arm-bases from three of the radials, viz. at one (outer) 

 side of each posterior, and at both sides of the anterior 

 radial, while the antero-laterals have none ; each process 

 has an offset like those of the anal interlocking with adja- 

 cent radials. Radial facets deeply curved, occupying a 

 median position except on the two posterior radials in 

 which the single outer processes occupy about half the 

 distal width of the plate, and the facets toward the pos- 

 terior side the remaining half. Anterior radial the 

 largest plate in the cup ; it and the two posterior radials 

 widen upwards, while the two lateral radials correspond- 

 ingly diminish in width, and by reason of the absence of 

 processes are shorter than the former; the right poste- 

 rior radial is the smallest, although with the radianal 

 added it is about equal to and slightly longer than the left 

 posterior. 



Arms unequal, uniserial, branching once, and appar- 

 ently very short; the two posterior and probably the 

 anterior arms have two primibrachs, while the antero- 

 laterals have but one; the axillaries are followed by 

 series of three or more subquadrangular brachials which 

 taper gradually. Anus and tegmen unknown. Stem 

 circular, axial canal unknown. 



Horizon and locality. Silurian ; top of chert in Laurel 

 formation. Adams Quarry near St. Paul, Indiana. 



