182 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



RemarJcs.— The type-specimen of PalxasterJiarrisi Miller is undoubt- 

 edly a Urasterella, and there are no characters other than size by 

 which this individual can be separated from U. grandis. Of about 

 the same age are three specimens in the Harris collection and another 

 in the University of Chicago, and all were originally referred to 

 P. harrisi. One of these is nearly again as large as the type, is about 

 one-half the size of U. grandis, and measures 49 mm. along the greater 

 radius. The only marked difference between P. harrisi and Z7. 

 grandis is the smaller number of adambulacral plates in the former, 

 a feature common to the yoimg of many fossil starfishes when com- 

 pared with the adults of the same species. In fact, the variation in 

 the number of these plates in the two largest examples (64 and 110) 

 is nearly as great as between the type of Palseaster harnsi (22) 

 and the smaller of the two largest specimens of U. grandis (64). 



U. grandis is closely related to U. pulchella (Billings) of the 

 Trenton limestone. Those species are, however, easily distinguished, 

 not only by the different geological occurrences, but in that U. grandis 

 attains a much larger and more robust growth. The latter has also 

 many more abactinal ossicles with longer nonarticulating spines, 

 and the adambulacral columns have from 60 to 110 plates, instead 

 of from 36 to 60 as in U. pulchella. U. grandis appears to be a 

 direct descendant of the latter and has varied only in attaining a 

 larger size and a greater number of plates. 



U. grandis is also closely related to Z7. ulrichi, and both are nearly 

 of one size. Tlio latter, however, has the rays highly convex abac- 

 tinally, the plates arc smaller but as strongly spinose, and there are 

 two columns of larger central plates, instead of one as in TJ. grandis. 

 In the latter in the mid-length of the ray there arc about 9 plates 

 in a column in 10 mm., while in TJ. ulrichi there are from 11 to 12 in 

 the same space. 



Cat. Nos. 40885, 40887, U.S.N.M. 



URASTERELLA HUXLEY! (Billings). 

 Plate 29, fig. 2. 



Stenaster huxleyi Billings, Geol. Surv. Canada, Pal. Foss., vol. 1, 1865, p. 213, 

 fig. 197. 



R = 58 mm., r = 5.5 mm., 11= 10. or. Width of ray at base, 6 mm. 



Original description. — " Deeply stellate, 4 or 5 inches across; body 

 small, loss than half an inch in diameter; rays long; flexuous, sub- 

 cylindrical, apparently angulatod along the medium line on the upper 

 side, uniformly tapering to an acute point. On the dorsal side the 

 rays are covered by a multitude of small subangular plates, each 

 from one-fourth to one-third of a line wide. The central part of the 

 body is not well preserved in the only specimen collected; but it is 



