350 PROCEEDINGS OF THE ACADEMY OF [1888. 



for considering Haplocriims and allied genera as larval forms. 

 Taking iiito consideration all the facts as now disclosed, and espe- 

 cially the non-existence of a central plate, we must admit the weight 

 of the evidence is in favor of the supposition that thf plates cover- 

 ing the ventral surface in Haplocrmus, and Allagecriniis are orals, 

 and that these orals are permanently closed in the Haplocrinidae 

 without the assistance of interradial plates. In accepting this as 

 probably the correct interpretation of those plates, we now recognize 

 also in Symbathocrinus and Plsocrmus five large orals as covering 

 the greater part if not all of the ventral surface, more or less similar 

 to those of Haplocrinus, though with a very different anal arrange- 

 ment in Symbathocrinus, and probably also in Pisocrinus. 



A still broader question remains to be considered, viz : the effect 

 of the late discoveries upon the classification of the Crinoidea, gener- 

 ally. In proposing the Palaeocrinoidea as a distinct order of the 

 Crinoids, we considered the presence of a subtegminal mouth, and 

 the closed state of the food-grooves, as the most important char- 

 acters by which they were distinguished from Mezozoic and more 

 recent forms. But it is evident that since the discovery of an open 

 mouth in the Palaeozoic genus Taxocrinus, we can no longer by this 

 means separate the earlier from the later crinoids. Carpenter did 

 not agree with us as to the importance of the subtegminal mouth, 

 and he proposed to separate the Palaeocrinoids from the Neocri- 

 noids principally upon other features which he discussed in detail in 

 the Challenger Report on the Stalked Crinoids, pages 149-155. A 

 sliirht examination will show that all these other characters meet 

 with so frequent and important exceptions in both groups, that it 

 is not safe to depend upon them. 



According to Carpenter, in the Neocrinoidea underbasals are re- 

 presented rarely, in the Palaeocrinoidea frequently (Challenger 

 Report, p. 149). Several years ago we discovered that there is a 

 regular alternation in the arrangement of the successive parts of 

 crinoids below the radials, which furnishes a most important guide 

 for distinguishing between monocyclic and dicyclic crinoids, by the 

 structure of the column and cirri. It was stated on page 7 of the 

 Revision, Part III, — with a most unfortunate transposition of terms 

 in printing, which we corrected on page 294, — and which may be 

 grai)hically expressed by the following sketch: — 



