130 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



various families, we find in the Batocrinidae directly above the plate x a 

 supplementary anal and an interbrachial at each side of it, exactly as in 

 most species of Cijathocrinus and Bendrocrmus, except that the interbrachials 

 of the two latter — i e., the plates corresponding to them — are incorporated 

 into the tube, but those of the Batocrinidse into the cup. Turning to the 

 Actinocrinidae, the plate x supports a supplementary anal in the second inter- 

 brachial row, but none in the first, a structure recurring in Graphiocrinus, 

 in which x is followed by two tube plates which take the place of the two 

 interbrachials of Actinocrinus. In the Dolatocrinites, however, in which x is 

 wanting, and the first row of the anal interradius is formed of a single plate, 

 this rests upon the sloping faces of two radials, thus occupying almost the 

 same position as the plate t {x of Bather) in Ectenocrinus, Hyhocrinus, and 

 locrinus. That the plate t in some of these forms is somewhat irregular in 

 position, leaning more to the right than to the left, is due to the asymmetry 

 of the right posterior radial. 



From these observations it appears that there is a close agreement be- 

 tween the anal plate and tube plates of the Fistulata on one side, and the 

 anal plate and interbrachials in the cup of the Camerata on the other ; and 

 we are led to believe that those plates respectively are homologous. Admit- 

 ting this, we have a much more satisfactory explanation of the anal plates of 

 the Fistulata than that given by Bather, whose views are totally at variance 

 with the structure of the Camerata, and are based upon premises which are, 

 to say the least, hypothetical. 



After agreeing upon the structure of Bendrocrinus and locrinus, that of 

 the other Fistulata is readily understood. Anomalocrinus is in a condition 

 similar to that of locrinus, but it has two compound radials instead of one 

 (Fig. 12). The plate x is unrepresented, and the tube, which is narrow, 

 rests within a notch formed by the sloping upper faces of the two posterior 

 radials. Nearly the same structure is found in Heterocrimis and Ectenocrinus 

 with three compound radials, and in Hyhocrinus with but one, and in all of 

 them the plate x is wanting. How Mr. Bather could conclude from the 

 structure of Ectenocrinus, locrinus or Hyhocrhius, three of the most primitive 

 forms, that x originated as a plate " morphologically corresponding to an 

 ordinary brachial," and that t could sink down to the basals, we do not 

 understand. It appears from his own diagram that the plate which he calls 

 x in Ectenocrinus is placed symmetrically between the two posterior radials, 

 resting as much on the one plate as on the other, but not touchino; the basals. 



