134 NEW YORK STATE MUSEUM 



Others. Both pedicels and spinelets seem, so far as size is con- 

 cerned, to be very Hke those already seen on the inner oral edges of ■ 

 the cover plates of this specimen. A study of the uncovered outer 

 faces of the cover plates shown in plate 6, figure i, is indicative of 

 similar conditions at their oral edges but the outer face itself seems 

 to negative the idea that these plates bore additional and larger 

 paxillae, in pairs, on more apical portions of this face, such as 

 Schuchert credits toU. grandis. The three specimens here 

 under study show no evidence for any spines or paxillae on the 

 cover pieces save at the inner and outer ends of the medial, oral 

 ridge. 



We are in a position now to note that if these specimens are to 

 be retained under Urasterella, the description of the genus must be 

 somewhat modified. Let us quote simply Schuchert's description 

 of the cover plates (1915, page 174) : '^Adambulacral plates very 

 numerous, coin-shaped, and arranged On edge with the actinal sur- 

 face pustulose. Each plate on its actinal surface bears two or three 

 short thick spines, and on its ambulacral side there is a similar 

 spine. Along the outer edge of these plates toward the abactinal 

 side there is another row of spines, in pairs, which are long and 

 slender, flat and longitudinally grooved on two sides. The adam- 

 bulacral columns terminate in small triangular plates of the oral 

 armature. In the young of U . u 1 r i c h i five very stout, short, 

 pointed spines (tori) are inserted inside of the plates of the oral 

 armature." 



None of our specimens show the actinal surface " pustulose," 

 but such structures are often easily removable. In plate 7, figure 2, 

 the spaces between the raised medial ridges of the cover pieces are 

 seen to be packed with fragments, suggestive of ova, which may be 

 removed pustules or separated beads of spines. In plate 12, figure 

 I, these ovoid blackened beads appear to be attached to both 

 vertical faces of the median, oral ridges and to have grown there- 

 from in a form resembling minute pufTballs. Traces of these 

 structures are also seen in figure 2 of this plate. 



The " two or three short thick spines " credited by Schuchert to 

 the oral ("actinal") surface of these plates, seem to be repre- 

 sented in our specimens by the single outer, oral pedicels bearing 

 two spinelets each, in U. medusa. 



On the inner oral edge or, perhaps more properly speaking, in an 

 excavated corner involving a part of the inner (ambulacral) face, 

 there appears to be a single spine in U. pulchella. In 

 U . medusa, however, the similarly attached spines seem to be 

 minute paxillae, each pedicel bearing two spinelets. 



