46 NEW YORK STATE MUSEUM 



probable composition of the actinal part of the rays are identical 

 with those of Lepidasterella and Helianthaster, with the evidence 

 from the visible interbrachial portion of the disk, we can not 

 escape the inference that Ptilonaster probably belonged to the 

 Lepidasteridae and may prove with better material to have been 

 a large Lepidasterella or a Helianthaster. 



It is also significant in this connection that the type specimen 

 while reported to have come from the Chemung group, is from the 

 vicinity of Cortland where the rocks were considered in the 

 earlier days of the Survey to be of Chemung age, but are now 

 referred to the Ithaca beds of the Portage group, which has also 

 furnished our species of Lepidasterella. 



Urasterella ruthveni (Forbes) mut. arisaigensis nov. 

 Plate 11, figures 5 and 6; plate 12, figure 3 



Description. Disk small, without interbrachial areas, rays 

 slender, very slightly widening in first proximal third, then regu- 

 larly tapering. R (length of ray), 14 mm; radius of disk, 2 mm. 

 Abactinal area of disk with distinct central large plate, from which 

 five ridges radiate along the median lines of the rays. These 

 ridges consist of the radial plates, their bases being formed by the 

 five basal radials. The next or second proximal radials of the 

 column are flanked by the basal marginal plates. The abactinal 

 side of the rays has a very characteristic and pretty aspect. The 

 median line is occupied by a crest formed by the radials which are 

 a little more tumid and larger than the remaining plates. The 

 radials, as well as all the other plates, are subquadratic in outline, 

 forming a very close pavement. They are flanked on either side by 

 three columns at the base and two columns near the tip. Of these, 

 those next to the radials are smaller than the outer columns; they 

 are the supramarginals. The third column, or second of the 

 ambitals, reaches only to the middle of the rays. The interbrachial 

 area is occupied by a single interbrachial marginal plate, on either 

 side of which is located a minute plate in regular quincunx position 

 with the adjoining ambitals, indicating that these may be the begin- 

 nings of other columns of ambital ossicles. All ossicles of the 

 abactinal side of the rays are arranged in very regular quincunx 

 and are all furnished with the unarticulated rods characteristic of 

 the genus. 



The actinal side exhibits rather narrow ambulacral grooves at 

 the bottom of which can be seen distinctly opposite, wedge-shaped 



