1916) The Ottawa Naturalist. 43 



p. 199), and "apparently immovable over the mouth region" 

 (1915, p. 212). In Blastoidocrinus we have also a closely cov- 

 ered condition of the similarly placed main food-grooves. We 

 have large covering plates which arch over the groove, and are 

 rendered immovable over both rays and mouth region by a series 

 of still heavier accessory plates, called by the author "apical or 

 anal pieces" and "wing plates," though for the fotmer the term 

 supraoral would be perhaps more appropriate. These ossicles 

 are figured in N.Y. State Museum Bulletin 107, plates 6 and 7. 

 In Blastoidocrinus a specimen the size of Styanoblastus would 

 have about 3 50 brachioles for a catching apparatus to supply 

 its covered main food-grooves. Bearing now in mind the fact 

 that both were stemmed Ordovician forms which lived in the 

 Ottawa sea, we must appreciate the difficulties which arise if 

 we deny brachioles to Steganoblastus. Why should a continued 

 stemmed existence in a similar environment cause the loss of a 

 specialized and efficient collecting apparatus, and leave only 

 the five main ways to the mouth, and these still closely covered 

 with covering-plates, immovable at least for the mouth region, 

 and for the older portions of the rays. 



There are other interesting points to be gathered from 

 Bather's description in which Steganoblastus resembles Blas- 

 toidocrinus. "The very deep folding of the plates," (1914, p.. 

 195), in adapical and interambulacral areas are in Blastoido- 

 crinus dtie to plate growth or development over hydrospires. 

 There is a "series of pores" between the outer ends of the floor- 

 plates and "just below the attachment of the cover-plates" 

 (1914, p. 198). 'The pores between the floor-plates pass 

 through into the thecal cavity" (1914, p, 199), entering hydro- 

 spires in both Blastoidea and Parablastoidea. "There is a 

 cover-plate to each floor-plate, and so far as can be ascertained 

 after prolonged preparation and study, the sutures between 

 the cover-plates coincide with those between the floor-plates. 

 Thus, the pores, which as already stated, lie just below the 

 attachment of the cover-plates, open under the sutures as in 

 Edrioaster ,, (1914, p. 199). Precisely this condition is to be 

 seen in Blastoidocrinus (N.Y. Museum Bulletin 149, plate I, 

 fig. 2). 



Of the outer border of the food-grooves Bather says: "The 

 suture between the cover-plates and the adambulacrals is flush, 

 and the curve of the cover-plates passes over, though with a 

 distinct bend, into that of the adambulacrals. The suture is 

 not a straight line, but a series of curves, the convex outer 

 edges of the cover-plates fitting into slight concavities in the 

 adambulacral margin. The position and number of the axial 

 ridges on this margin indicate that the original adambulacral 



