39 



SCAPHIOCRINUS ARROSUS, n. Sp. 



Plate VI, Fig. 5, azygous view of calyx and arms. 



All the plates of the calyx and arms are angular and present 

 a very rough aspect. The plates of the calyx, though small, 

 are deeply sculptured. The calyx is low, less than half as wide 

 as high. The column is obscurely pentagonal, and composed 

 near the calyx of thin plates radiately furrowed near the outer 

 circumference. 



Basals small, hidden by the column. Subradials small, wider 

 than high, directed outward, hexagonal, except the one on the 

 azygous side, which is truncated at the top and heptagonal, 

 each one is produced into an angular node, at the central part. 

 First radials pentagonal, about half as high as wide, sharply 

 angular, or having a ridge at the upper part and a radiating 

 ridge from the central part to each adjoining subradial. Hori- 

 zontally truncated the entire width of the plate on top, where 

 the suture is gaping. Second radials quadrangular, about half 

 as long as wide, sharply angular in the central part; sutures 

 gaping. Third radials pentagonal, nearly as high as wide, axil- 

 lary, sharply angular in the central part, upper sides very steep 

 and each supporting an arm. 



The bifurcation of the arms is not uniform, in the different 

 rays. The one on the left of the azygous area bifurcates on the 

 fourth plate, while the four on the right of the azygous area 

 bifurcate on the sixth plate. One of the arms does not bifurcate 

 again, but the other one bifurcates once, though not at uniform 

 distances from the first bifurcation. This method of dividing 

 the arms gives to the species, in the upper part, thirty arms. 

 The arms are angular externally, and composed of slightly cunei- 

 form plates that bear coarse pinnules. 



The azygous plates are sculptured, the central part of each 

 being most prominent, and arranged in alternate order, the first 

 one is inserted obliquely between the subradial and a first radial. 



The calyx of this species resembles the calyx of Scaphiocri- 

 nus bonoensis, but the arms are not half as numerous and are 

 wholly different, after the first division. We do not know of 

 any other species with which it is necessary to compare it. 



Found in the Keokuk Group, in Washington county, Indiana, 

 and now in the collection of Wm. F. E. Gurley. 



