500 HERRICK E. WILSON 



the anal series. The base throughout this family is pentagonal, 

 and the basals number either five, four, three, or one. When five 

 basals are present the basal sutures meet the radials in the normal 

 manner. When four basals are present either the anterior or left 

 anterior suture is missing, and when only three basals are present 

 the sutures meet the anterior, left-anterior, and right-posterior 

 radials. 



The Calyptocrinidae have throughout a pentagonal base and 

 only four basal plates, and the anal plates are entirely missing. 



In considering these families the question arises as to whether 

 the base has been pentagonal throughout its whole phylogenetic 

 history or whether there has been a hexagonal stage, as in the 

 Batocrinidae and Actinocrinidae. 



The Platycrinidae and Hexacrinidae are characterized by having 

 the ambulacral grooves and lower brachial plates but slightly 

 incorporated in the calyx. The orals in the simpler forms are well 

 developed, and the base is either pentagonal or hexagonal. In 

 the Platycrinidae no anals have been positively determined, and 

 the base is pentagonal. Throughout this group there are ordinarily 

 but three basals, five in youth and sometimes but one in age. 

 Two of the basals are large, the third smaller. In the Hapalo- 

 crinus. 1 the smaller basal is the right-anterior one, and the basal 

 sutures meet the anterior, right-anterior, and the left-posterior 

 radials, as in StcpJianocrinus. In the other genera of Platycrinidae 

 the left-anterior basal 2 is the smaller, and the basal sutures meet 

 the anterior, left-anterior, and right-posterior radials. In the 

 Hexacrinidae there are usually three, or two, equal basals, some- 

 times only one. 5 The base is hexagonal and the anal plate well 

 developed. The basal sutures in the three-basal forms meet the 

 antero-lateral radials and the anal plate; in the two-basal forms 

 the sutures meet the anterior radial and the anal plate. 



A discussion of the monocyclic Inadunata as a whole cannot 

 now be undertaken, but certain species of Larviformia which in 

 their development illustrate very clearly, even diagrammatically. 



1 Ref. 2i, pp. 94-110. 



2 Exceptions are noted on p. 507 in the description of Fig. 5, Xo. 6. 



3 Ref. 0, p. 15S. 



