178 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



In regard to Protasteracanthion Stiirtz, see remarks under Uras- 

 terella asperula, and for Salteraster Stiirtz see U. asperrima. 



UrastereUa differs from Stenaster as redefined in this work in having 

 long, slender, flexible rays which are never short and petaloid as m 

 the latter genus. Again, the adambulacral pieces of UrastereUa are 

 very numerous, thin, and coin-shaped, while in Stenaster they are few 

 in number and comparatively thick; the ambulacral plates are 

 wholly different. 



The long, slender and flexible rays, the apparent absence of in- 

 framarginal columns, and the absence of distinct interbrachial 

 plates (these are not the same as the single axillary pieces seen in 

 U. asperula) at maturity readily distinguish this genus from all other 

 Paleozoic genera. 



For the origin of UrastereUa see U. ulricJii. 



Eoactis. — After this book was completed appeared the work of 

 Spencer, with the new genus Eoactis. It is probable that the genus 

 is good and can be distinguished from UrastereUa, but the necessary 

 comparisons can not now be made. 



URASTERELLA PULCHELLA (Billings). 

 Plate 28, figs. 3, 4; plate 30, fig. 6. 



Palseaster pulchellus Billings, Geol. Siirv. Canada, Rep. Progress for 1853-1856, 



1857, p. 292. 

 Stenaster pulchellus Billings, Geol. Surv. Canada, Can. Org. Rem., dec. 3, 1858, 



p. 79, pi. 10, fig. 2. — Wright, Mon. British Foss. Echinod., Oolitic, vol. 2, 



pt. 1 (Palaeontogr. Soc. for 1861), 1862, p. 28. 

 UrastereUa (Stenaster) pulchellus Hall, Twentieth Rep. N. Y. State Cab. Nat. 



Hist., 1868, p. 289; rev. ed., 1868=1870, p. 332. 



The largest specimen from Middleville, New York (Hall collection), 

 measures: R = 52 mm., r=«ll mm., R = 4,8r. An individual of the 

 usual size from Trenton Falls, New York CNIus. Comp. Zool., No. 31), 

 measures: R = 30 mm., r = 4 mm., R = 7.2r. One from Ottawa 

 (Geol. Surv. Canada collection) measures: R = 25 mm., r = 4 mm., 

 R = 6.1r. The smallest specimen seen (Mus. Comp. Zool., No. 36) 

 measures: R = 7 mm., r = 1.5 mm., R = 4.7r. Width of rays at 

 base in mature examples from 4.5 mm. to 7 mm. 



Original description. — "Diameter, 2 J inches; rays subcylindrical, 2^ 

 lines in width at the base, with a length of 1 inch; disk 3 J lines in 

 diameter; grooves narrow, bordered thi-oughout by narrow oblong 

 plates, nme in the length of two lines ; the length of these plates in a 

 direction transverse to the rays is about 1 hne; near the disk there 

 appears to be but one row of marginal plates." 



Formation and locality. — Restricted to the Trenton limestone. 

 Most abundant at Trenton Falls, New York. From this locality 



