1886.] NATURAL SCIENCES OF PHILADELPHIA. TT 



basal regions, nor even of the arms, we are not in a position to 

 give a satisfactory definition of the group. 



In order to obtain some additional information, we applied to 

 our friend, Walter R. Billings, who, with his usual kindness, has 

 furnished us the diagrammatic sketch of the type-specimen, 

 which is reproduced on Plate 9, fig. 5. The suture lines of all 

 plates above the primary radials, vertically and horizontally, are 

 provided with a kind of minute pores ; which, it seems to us, 

 indicates a union by syzygy, and not by articulation, and that 

 the arm structure was altogether different from that of the other 

 Articulata. Mr. Billings informs us that " the plates are all 

 joined together, but where the strain in crushing has acted upon 

 the specimen, the cracks or gaping sutures are preferably on the 

 lines of the grand divisions, i. e., the lines dividing the arms 

 from one another and from the anal series." This parting of the 

 plates, however, does not indicate necessarily a leaf-like struc- 

 ture of the rays, as in the case of Grotalocrinus^ for all plates 

 united by syzygy, as a rule, come easily apart. 



Mr. Billings informs us that tlie ridges of the column are inter- 

 radial in position, which confirms the supposition made by us 

 (Part I, p. 36 \ that Gleiocrinus possesses underbasals, and that 

 the so-called basals of E. Billings are interradials. He also states 

 that the lowest visible circlet of plates " apparently overlaps the 

 column, instead of passing under it," which shows that the base 

 must have been concave, with ample space for the basals and 

 underbasals to lie concealed from view. We have indicated the 

 basals and underbasals in the diagram by dotted lines. 



It will be useful to give an amended 



General Diagnosis. General form obconical ; with bilateral 

 symmetr3^ Base dicyclic. Underbasals probably 3, minute or 

 rudimentary. Basals probably 5, small and hidden by the 

 column. Primary radials 3X5, increasing in width upwards, 

 supporting several superior orders of radials, dichotomizing 

 frequently and uniformly, and interlocking with those of 

 adjoining rows. 



The rays and their divisions are laterally connected, without 

 the intervention of interradial plates, except at the anal side 

 and along the first primary radials. The first radials are much 

 smaller than the succeeding ones, and separated from one another 

 by a comparatively large pentangular interradial. The inter- 



