92 PROCEEDINGS OF THE ACADEMY OF [1886. 



delicate jDlates, which are bent longitudinally so as to form an 

 angle, and each plate extends to, and forms a part of, two of its 

 sides. The interradials alternate with radial dome plates, which 

 are even smaller, angular above. 



The summit is closed by the proximals and oral plate, all of 

 which are much larger than the interradials. The proximals con- 

 sist of four comparatively large, nodose plates, which enclose 

 toward the azygous side three scarcely convex, smaller ones. 

 The oral plate is the largest piece of the ventral side, it forms 

 an inverted cup, containing radiating grooves along the inner 

 floor, which lodged the ambulacra. 



Arms five, long, simple; closely folded together and forming a 

 narrow, cylindrical body. They are composed of a large number 

 of quadrangular joints, with parallel sutures, and are provided 

 with a deep ventral furrow, but apparently have no pinnules. 

 The first brachial differs somewhat in form from the others ; it is 

 always higher, extending to the level of the oral plate ; also wider, 

 but not quite as deep. Its proximal face is provided with a 

 muscular appendage, which corresponds with that of the radials; 

 its distal end, however, shows neither ridge nor fossae. The 

 higher brachials in all probability were united by suture, and the 

 arms moved as a body upon the radials. The articular faces of 

 the latter are provided near their outer margin with a transverse 

 ridge (PI. 5, figs. 12, 13), extending to the whole width of the 

 plate, with a transverse axial canal. The ventral furrow is deep, 

 has a longitudinal groove along the inner floor, and rib-like pro- 

 jections alternating with grooves along the inner walls. The 

 sides of the furrow are lined by two rows of short transverse 

 side-pieces about eight to each side of the arm joint alternately 

 arranged, which leave a zigzag median opening along the whole 

 length of the arms. There are also lateral pores, one to every 

 side-piece, and these connect with, and form the upper end of, 

 the lateral furrows at the inner walls of the arm grooves to which 

 we alluded. The lateral faces of the arm joints are provided 

 along their outer side with shallow slanting grooves (PI. 5, figs. 

 12, 13), and these agree in number with the pores. It seems to 

 us very probable that, b}' means of these grooves, the ventral 

 furrow was brought in contact with the surrounding element, as 

 the arms in this genus are so closely folded together, that with- 

 out them no communication was possible. 



