44 



Family PTEROTOCRINID.E. 



PTEROTOCRINUS WETHERBYI. n. Sp. 



Plate IV, Fig. 6, azygous side of an almost perfect specimen 

 except the interbrachial plates are broken off; Fig. 7, 

 basal view of another specimen, azygous side down, 

 and having the interbrachials broken: Fig. 8, 

 summit view of the same showing the small 

 plates at the apex of the vault; Fig. 

 9, view of another specimen with 

 the arms broken off so as to 

 show the furrowed vault 

 and sides of interbra- 

 chials that are some- 

 what broken. 



Species medium size. Calyx low, saucer-shaped, between two 

 and three times as wide as high, broadly constricted in the re- 

 gion of the primary radials. Surface finely granular. Column 

 small, rouud, deeply inserted and having a very minute central 

 canal. 



Basals two, each pentagonal, by reason of being slightly trun- 

 cated, at one angle, by the azygous plate, and together, forming a 

 low, subpentagonal cup, notched at one angle, by the azygous 

 plate, and having a deep central depression for the insertion of 

 the column, which has a diameter equal to about one-fourth the 

 width of the basal pentagon. The columnar cavity is funnel- 

 shaped and has a rather sharp or angular rim. First primary 

 radials of unequal size and by reason of the truncation of two of 

 them by the azygous plate very unlike in outline. They are from 

 three* to four times as wide as long, three heptagonal and two 

 hexagonal. Second primary radials small triangular plates resting 

 on the middle part of the straight upper face of the first radials 

 and each occupying from one-fourth to one-fifth of the width of 

 the superior face of a first radial and supporting on each sloping 

 lateral side part of a first secondary radial. There is only a sin- 

 gle secondary radial in each series and it is more than twice as 

 wide as high, irregularly pentagonal, and rests its part upon the 

 first primary radial but rarely if ever extends to the superior lat- 

 eral angle of it, and bears upon the superior side a tertiary series 



