12 • Trans. Acad. Sci. of St. Louis. 



by which it connects with the annulus centralis or central ring 

 of the deltoid pieces, resting thereby on two deltoid pieces; 

 see Fig. 2. The center of these pieces is perforated by a fine 

 channel in its entire length, bifurcating at its base to connect 

 with the transverse channel of the deltoid base-portion, form- 

 ing thus a pentagonal ring around the central opening. The 

 size of these channels is such that it seems hardly possible 

 that they could serve for the water vascular system. It seems 

 more probable that they contained the nervous system, giving 

 a similar arrangement to what we find in higher forms like 

 Asteroids; see Fig. 4. 



The little beak-like process where the lancet piece connects 

 with the deltoid is laterally grooved to form with the corre- 

 sponding groove of the deltoid, the ovarian or genital aperture 

 except in species where the deltoid piece is perforated, as in 

 G. norwoodi. 



POKAL PIECES. 



The triangular groove which is formed by the outer margin 

 of the lancet piece and the inner margin of the fork piece sinus 

 is filled with little pieces corresponding to this groove, which 

 were called most appropriately poral pieces by Dr. Roemer. 

 This name has been changed to side plates by R. Etheridge, Jr., 

 and P. H. Carpenter,* which term is also adopted by C. R. 

 Eastman. t The reason given for the change of this name is 

 not a logical one and shows that the nature of the pieces is 

 not thoroughly comprehended. Are perhaps the poral open- 

 ings not constructed by the poral pieces? Does not the name 

 poral piece indicate the nature better than the new name? 

 What benefit is to be derived from the new name ? They are of 

 a triangular form, corresponding to the groove which they 

 occupy. They are inserted edgewise so that the thickness of 

 these pieces forms their outer exposed surface; see Fig. 5. 

 These pieces have on both sides of their outer lateral margin 

 a little semi-lunar groove, which with the adjoining one 

 forms the pore-opening, and, in no case, are these pieces 



♦ Catalogue of the Blastoidea. 

 t Text Book of Palaeontology. 



