1886.J NATURAL SCIENCES OF PHILADELPHIA. 91 



basin-shaped. Basals three, forming a shallow cup, which is 

 slightly excavated for the reception of the column. They are 

 composed of two larger equal pieces which are pentangular, and 

 a smaller quadrangular one ; the latter placed to the left of the 

 anterior interradius as in Platycrinus. 



Radials nearly equal, subquadrangular ; the basi-radial suture 

 sligbtl}^ angular ; width much wider above than below. Their 

 upper side forms a straight, horizontal line, except at the right 

 postero-lateral radial, of which the left upper end is sloped off 

 for the reception of an anal piece. The anal plate rests com- 

 pletely upon this one radial, occupying about one-fourth of its 

 upper width. The radials are provided with large articular facets, 

 which, extending inwards and upwards, form jointly at the ventral 

 side of the calyx a sharply angular pyramid with re-entering 

 angles. The upper end of this pyramid is truncated, and con- 

 tains a good-sized opening in the centre, which in perfect speci- 

 mens is completely covered by the interradial and summit plates. 

 The lateral margins of the facets meet at their lower ends, except 

 at the azygous side, where they are separated by the anal plate ; 

 along their upper ends, however, they stand apart, and form 

 rather conspicuous clefts. Each facet is divided vertically by a 

 narrow sinus, ^ and the two halves of the plates or the limbs, as 

 they might be called, at their upper end form an ambulacral 

 opening. 



The interradials are unusually small, wider than high ; those 

 at the four regular sides resting against the upper face of two 

 limbs of adjoining radials. The number of interradials at the 

 azygous side cannot be ascertained in our specimens, as the parts 

 connecting the anal plate with the ventral surface of the calyx 

 were not preserved. The anal plate stands in line with the first 

 brachial, it has the same height but not its width, and is suc- 

 ceeded by a slender tube which follows the whole length of the 

 arms. Hall has figured a second anal plate, triangular in form ; 

 this, however, constitutes the lower portion of the first plate of 

 the tube, which always takes a sharp inward turn, leaving only a 

 small triangular space exposed externally between the arms. 

 The tube is composed of five rows of quadrangular, rather 



1 These sinuses, wtiicli look somewhat like suture lines, give to the 

 muscle plates the appearance of representing separate pieces, interradially 

 disposed, and this led us at first to regard them as oral plates. 



