MEDUSASTER. 205 



and large central oval bead-like tubercles are well shown in one of the specimens in 

 the Museum of Practical Geology. The oral plates are not distinct ; they are 

 probably either very small, or have their surface divided by a depression. The 

 arms seem unusually long for this genus ; in two of the specimens (PI. XXVI, 

 tig. 4, and PL XXIX, fig. 3) the arms appeared at first sight shorter and more 

 conical, but a slight development of the specimens (after they had been drawn) 

 showed that their arms were really longer than at first appeared, and there seems 

 little doubt that their semblance of shortness is due to their being twisted and 

 covered with matrix. 



Affinities. The length of the arms and the much fewer number and larger 

 size of the rows of plates appear to distinguish this species from P. asperrimus, 

 Salter. 1 From P. coronella, Salter, 2 it seems separated by the absence of a corona, 

 and from P. obtusus, Forbes, sp., 3 and P. Ruthveni, Forbes, sp., 4 by the character 

 of the ornament. Most if not all of the species of Palseaster described by Hall 5 

 in his Twentieth Annual Eeport are distinguished by the much greater shortness 

 of the arms. 



Asterias asperula, Ferd. Romer, 6 seems, on the other hand, to be still slighter in 

 shape, and to have relatively longer arms. From its state of preservation the 

 figures are not easily compared with ours, but the description indicates that there 

 were two alternating central rows of plates instead of a single large central row, 

 as in the present species. 



The arms of P. Caractaci, Salter, are much shorter, and the surface arrange- 

 ment quite different. 



2. ORDER EUASTERLE, Zittel, 1895 (= ASTKRLE VBRJE, Bronn). 



1. Genus MEDUSASTER, Stiirtsi, 1890. 

 1. MEDUSASTER PARVUS, n. sp. Plate XXXVII, fig. 4. 



Description. Animal minute, with a large round disc and sixteen arms. Disc 

 rather thick, flatly cushion-shaped, and apparently covered by numerous large 

 nodular plates. Angle-ossicula apparently very large and long, leaving in the 

 cast long triangular ridges, which extend from the point of junction of the bases 



1 1857, Salter, ' Ann. Mag. Nat. Hist.,' ser. 2, vol. xx, p. 325, pi. ix, fig. 1. 



2 Ibid., p. 326. 



3 1849, E. Forbes, Mem. Geol. Surv.,' Decade 1, p. 2, pi. i, fig. 3. 



4 Ibid., p. 1, pi. i, fig. 1. 



5 1867, Hall, ' Twentieth Ann. Eeport Eegents Univers. N. .,' p. 283, pi. ix, figs. 14. 



6 1863, Ferd. Eomer, ' Palseontographica,' vol. ix, p. 146, pi. xxiv, figs. 15; pi. xxvi, fig. 6; 

 and pi. xxvii, fig. 1. 



