Il6 NEW YORK STATE MUSEUM 



A series of sections or the gradual grinding down of the oral 

 portion of the specimen figured in plates I, 2 and 3 would no 

 doubt throw much light on this subject but it seems better to 

 await the finding of other fragments rather than to further muti- 

 late so perfect and unique a specimen. 



Views of these fused anal plates may be seen in plate 7. Fig- 

 ures a to o represent the under surfaces of a series arranged 

 according to probable age, an ontogenic series. The piece is at 

 first rather thin, its vertical axis less than half of its horizontal 

 and showing no sign whatever of a central perforation. The 

 piece at a is tilted a little to show its thinness. Figures b, c, d, 

 e and g show the beginnings of an indentation which becomes 

 very marked as the piece increases in age. The more mature 

 pieces 1 and o show also other indentations. The piece has 

 grown principally by additions to its under surface and to a less 

 extent to its edges. The deeper indentation is rather suggestive 

 of a bend of the rectum, the anal interradius being perhaps the 

 lower in the figure. The interradial indentations in figure o may 

 be the impressions of plates covering the peristome. Figures 

 p, g and x are of upper surfaces showing the grooving caused 

 by increased upward growth due to more extended additions to 

 the plate edges as in the wing plates. Figure g is the anal piece 

 of a regularly four rayed or tetramerous specimens while figure x 

 is of a specimen having its anal piece of six fused plates and 

 possessing a small sixth ray. The vertical axis of these pieces 

 is increased in some specimens to nearly three times their 

 horizontal diameters. 



Stem. Billings described the stem as " round with an alimen- 

 tary canal so small that often the detached joints seem to have 

 no central perforation . . . the flat faces of the separate 

 joints exhibit strong radiating striae." The diameter of the 

 stem of the specimen shown in plate 1 is 3 mm while the joints 

 themselves have a thickness of about 1.4 mm as may be seen in 

 plate 3, upper figure. The last joint left on the stem fragment of 

 this specimen seems to be split across in a direction nearly parallel 

 with the plate face and while it shows a central perforation about 

 .3 mm across, or one tenth of that of the stem diameter, it does not 

 show the strong radiating lines mentioned by Billings. Associated 

 with the fragments of this species, however, are stem joints and 

 roots shown in plate 7, figures r to w, which do show these lines. 

 These stem joints are not abundant here and this would indicate a 

 short stem. I have found no evidence as yet that the stem pene- 



