242 PROCEEDTNGS OF THE ACADEMY OP [1881. 



Impossibility. The species of this genus are so numerous that a 

 sub-division would be ver}' desirable, but even a subgeneric sepa- 

 ration, based upon the presence or absence of an anal tube, upon 

 which other genera of this family have been successfully divided, 

 cannot be practically carried out at present, for the reason that 

 these parts are known only in comparatively few species, and we 

 have been unable to discover an}' additional characters by which 

 to separate the two forms. We have, however, added Pleurocrinus 

 in brackets, wherever the species is known to possess a simple 

 opening, and it may be said that, as a pretty general rule, species 

 of their kind have a more discoid form, while those with a tube 

 have a more elongate body ; but there are exceptions in both cases, 

 and often the facts are exactly the reverse. 



Generic Diagnosis. — Body spheroidal; low discoid to elongate. 

 Calyx composed of basals and first radials, without anal plates 

 intervening ; all succeeding radials embraced in the free rays ; 

 surface of plates variously ornamented ; symmetry almost equi- 

 lateral. 



Basals three, unequal ; one quadrangular, the other two pentan- 

 gular and twice as large. The}"^ are cemented together b}^ their 

 sides and form a flat disk, or a more or less shallow cup, the 

 smaller basal being located below the suture between the anterior 

 and left lateral radials. Primary radials 2X5; the first very 

 large, about quadrangular in outline, the second small, triangular 

 or pentagonal, resembling an arm plate in form. Second radial 

 inserted upon the excavated upper margin of the first, or upon 

 this and a projecting callosity or thickening of the margin. The 

 plate is sometimes so small that even both radials of the second 

 order rest within the excavation of the first plate. The orders of 

 radials vary in number, corresponding to the number of arms in 

 the species ; each order consisting of two plates, both wider than 

 high, the second bifurcating. All the radials from the second 

 - primar}' up, are placed into free rays, from which the arms are 

 given off alternately from opposite sides, with two arms to the last 

 bifurcation. 



Arms long, rather heavy, composed of a double series of plates, 

 which have the same style of ornamentation as the plates of 

 the calyx. In the younger stage, the arms are composed of 

 single wedge-form joints, giving off pinnules in a zigzag form. 

 Pinnules long, slender, composed of rounded joints, closely packed 



