238 PROCEEDINGS OF THE ACADEMY OF [1881, 



sides. This plate occupies not more than one-fourth to one-third 

 the width of the first radials, and supports on its upper ^sloping 

 margins the secondary radials. Secondary radials 2 X 5, enveloj)- 

 ing the little bifurcating plate entirely except below. The^'^ are 

 comi)aratively large, pentagonal to heptagonal, meeting by their 

 short inner sides above the apex of the small bifurcating plate, 

 and resting with their lower sides upon the upper margin of the 

 first radial, filling the gi'eater part of it. In some cases they 

 touch with their outer edges the interradials, and support upon 

 their long upper sides several small plates which pass gradually 

 into the arms. In other cases there is on either side of these 

 plates, and between them and the interradial, another plate of 

 about the same size, which sometimes rests also partly on the first 

 radial, and forms the first of a series of three tertiary radials. 

 which support the outer arm on each side of the ray. One, and 

 sometimes two similar tertiary radials support each of the inner 

 arms of the ray. In forms like the last, the secondary radials 

 seem to be bifurcating plates, supporting on each upper sloping 

 face a series of tertiary radials leading to an arm. 



Arms twenty, sometimes perhaps only ten ; composed of a double 

 series of interlocking joints, either throughout their entire length, 

 or all except near the base, where there are sometimes single 

 cuneiform joints passing gradually into a double series. Arm 

 furrow deep and wide ; pinnules long, composed of round joints, 

 somewhat contracted in the middle and widening toward the 

 articulations. 



Interradial plate large, higher than wide, sxipported upon the 

 upper sloping corner of the first radials, and connecting the 

 secondary and frequently the tertiary radials with the body. 

 Posterior side of calyx in no way distinct from the other sides. 



Vault low, hemispherical, composed of a larger number of 

 plates than usually found in this family ; plates small, particu- 

 larly the radial dome plates. These are generally formed into 

 narrow ridges, which bifurcate twice within the bod}-. Inter- 

 radial dome plates larger than the radial ; apical plates not 

 prominent and identified with difficulty ; interpalmar spaces 

 paved with small pieces. Anus subcentral, tubular, or perhaps 

 in form of a simple opening (?), 



Column round, composed of rather large joints alternating 



