1890.] NATUKAL SCIENCKS OF PHILADELPHIA. 383 



After detenu ining- the structure of Dendrocrinus and ^locrinns 

 the other genera are readily understood. Anomalocrinus is in a 

 similar condition to locrinus, but has two compound radials in place 

 of one. As in the case of locrinus the plate X is unrepresented. 

 Its tube, which is narrow, rests within a notch formed by the slop- 

 ing upper faces of the two ])Osterior radials, the lower plate touch- 

 ing the first costal. Almost the same structure we find again in 

 Heterocrinus and Ectenocrinus with three compound radials, and in 

 Hybocrinus with but one. We cannot understand how Bather on 

 p. 330 of his paper could conclude from the structure of Ecteno- 

 crinus, which he has regarded as one of the most " primitive forms," 

 that X " originated as a plate morphologically corresponding to an 

 ordinary brachial." His own diagram shows that his plate X in 

 Ectenocrinus is placed symmetrically between the two posterior 

 radials, resting as much on the one plate as ou the other. In his 

 diagram of Heterocrinus heUevillensis the plate is not correctly rep- 

 resented. A comparison with Walter Billings' figures (Trans. Ot- 

 tawa Field Naturalist's Club, 1883), and ours (PI. X, fig. 8), shows 

 that it resembles in form and position that oi Ectenocrinus, (fig. 9). 

 Like that it rests upon the sloping upper faces of both posterior 

 radials, and not on the plate to the right only. The plate in Hybo- 

 crinus occupies almost the same position, and we confess we fail to 

 see how the structure of either of these genera helps to prove that 

 the plate is a modified brachial. We think the evidence derived 

 from them shows conclusively that it is an interradial plate. If the 

 ventral sac represented a modified arm, we should like to know to 

 which ray the plate in Heterocrinus and Ectenoei'inus belongs, 

 whether to the right or to the left? In Dendrocrinus casei, in which 

 the case is somewhat complicated, we would have three modified 

 arms, one to the right, one to the left, and one supported by the 

 plate X. Dendrocrinus caduceus (PI. X, fig. 11) would have vari- 

 ously two or three such arms, two resting upon the upper sloping 

 faces of adjoining radials, and both supported by the plate X. Still 

 more inconceivable would be the case of Hybocrinus in which the 

 so-called '" brachianal" supports numerous small, irregularly ar- 

 ranged pieces forming a short protuberance. 



In alluding to the anal structure of the Camerata, it has been 

 pointed out that in the Actinocrinidae the first anal plate rests be- 

 tween the radials, contrary to the Melocrinidae, in which the lowest 

 anal plate rests within the second row of interradial plates, and all 



