126 NEW YORK STATE MUSEUM 



in revealing the same. From these circles or parts of such there 

 runs a channel which becomes less wide and deep and which crosses 

 diagonally from one plate to the next one on the proximal side. 

 On the latter plate the channel is soon lost. Between the convex 

 (in section) inner ends of the floor plates there is a preserved mass 

 of organic fibers, most of which run parallel with the axis of the 

 arm. We are here probably dealing with a portion of the radial 

 branch of the water- vascular system and the more delicate side 

 branches have been lost by weathering. At this level the inner 

 ends of the floor plates seem to be separated, and this appearance 

 led me at first (1914, page 5, lines 3-4) to assume that here at 

 least was a line along which a single row of podial openings might 

 have found exit. A similar aspect doubtless led Schuchert (191 5, 

 page 174) to give as a character of the genus Urasterella that 

 " Medially the columns loosely adjoin." In plate 9, figure 3, the 

 great depth of the inner sutures of the floor plates and their close 

 contact would seem to negative such an assumption. So also would 

 the position of the median water vessel clearly shown in cross 

 section in figure 2 of this plate. The delicate lateral branches of 

 this vessel had to pass over the oral surface of the floor plates to 

 reach the position of the podia and podial sacs already noted. For 

 further evidence of close suture at the inner ends of the floor plates, 

 see our plates 2 and 3 and the photomicrograph, X20 dia., given 

 in Hudson, 191 5. 



Another detail of the floor plates requires attention. In plate 2, 

 figure I, the second, third, fourth and sixth floor plates of the upper 

 row have had their outer faces vertically channeled to correspond 

 with similar channels on the inner faces of the inframarginals. 

 The pores so formed have a diameter (measured on plate 4, third 

 floor plate) of .05 mm. From many of the outer arm faces these 

 channels are decidedly absent. Papulae were numerous on the 

 apical surface of the genus as shown in Schuchert's drawing of 

 the apical surface of a young U . u 1 r i c h i (1915, plate 30, figure 

 6). We have in U . medusa an example of a fringe of papulae 

 issuing between the inframarginals and the covering plates. When 

 the food groove was closed these papulae would appear on the oral 

 surface; when the arm was open they would appear on the apical 

 surface. In plate 3, figure i, floor plates 6, 12, and 13 of the 

 right column show small pores penetrating the outer end of the 

 plates. These are seen also in the right column of figure 2, floor 

 plates 2 and 5, and elsewhere. Note also what appears to be a 

 pore passing between floor plates 8 and 9 of this series and in still 



