294 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



plates, very numerous actinal intermediate pedicellariae. The pedi- 

 cellariae of P. nidarosiensis are of the bivalve, sessile type charac- 

 teristic of Ilifpastei^ia^ whereas in cycloplax they are of the en- 

 trenched 2-jawed sugar-tongs type, similar to those of Nymphaster^ 

 and other related genera. If P. hehes Verrill is distinct from ni- 

 darosiensis it will differ from cycloplax in practically the same char- 

 acters as P. nidarosiensis. P. planus Verrill lacks pedicellariae en- 

 tirely, and has fewer abactinal granules to the plate, wider and less 

 tumid superomarginal plates, and only 3 or 4 furrow spines. 



Genus PONTIOCERAMUS Fisher. 



Pontioceramus Fisher, 1911c, p. 420. Type, P. grandis Fisher. 



Diagnosis. — Stellate, with a large disk and relatively short rays. 

 Related to Plinthaster Verrill, but differing in having the surface of 

 the abactinal plates perfectly smooth, not covered with minute 

 bosses, in having the plates of the papular areas low-tabulate, and 

 the adambulacral plates with an angular furrow margin armed with 

 numerous short stubby spinelets; no conspicuously enlarged sub- 

 ambulacral spine on distal part of ray. Abactinal and marginal 

 plates bordered by a single series of small granules, the latter also 

 with some on lateral face of ray, all flush with level of plate. Last 

 few superomarginals in contact medially. Actinal intermediate 

 plates reaching far along ray, closely granulate, and with small bi- 

 valved excavate pedicellariae about as high as wide. Adambulacral 

 plates proxiihally very narrow, distally becoming wider; with a large 

 subambulacral toothed bivalved pedicellaria, and 10 or 11 furrow 

 spinelets in angular series. No smaller secondary abactinal plates. 



PONTIOCERAMLS GRANDIS Fisher. 



Plate 77, fig. 3 ; plate 78, fig. 3 ; plate 83, fig. 4 ; plate 93, figs. 4, 4a-&. 



Pontioceramus grandis Fisheb, 1911c, p. 421. 



Diagnosis. — Size large; stellate, with a large disk, shallow inter- 

 brachia, and short bluntly pointed rays, arcuately tapering from a 

 very broad base to an attenunate extremity, the last 5 to 8 supero- 

 marginals being in contact; abactinal plates numerous, with very 

 smooth surface bordered by immersed granules flush with surface, 

 the central and radial areas having the plates low-tabulate and 

 hexagonal; marginal plates conspicuous, decreasing in size gradu- 

 ally, and bordered by flush granules; actinal intermediate plates nu- 

 merous, granulate those nearest furrow with 1 or 2 small, denticu- 

 late, bivalved pedicellariae; furrow spinelets 11 or 12, short, stout, 

 blunt, forming an obtusely angular series, the apex varying in posi- 



