REVISION OF PALEOZOIC STELLEROIDEA. 



91 



MESOPAL-EASTER BELLULUS (Billings). 



Text fig. 7. 



Petraster bellulus Billings, Geol. Surv. Canada, Pal. Foss., vol. 1, 1865, p. 393, 

 fig. 368.— Miller, N. Amer. Geol. Pal., 1889, p. 269, fig. 389. 



Original description. — -"Deepl}' stellate, about 18 lines across; disk 

 5 lines wide; width of rays, at the base, half the width of the disk, 

 uniformly tapering to their extremities; ambulacral grooves, narrow 

 and deep, with about 30 adambulacral plates on each side. These 

 plates are strongly convex and nearly square [distally, but proxunally 

 are wider than long]. Outside of these there is a row of [about 21 

 infra] marginal plates, which appear to [actually do] extend to the 

 extremities of the rays, but on this point there is some doubt, as the 

 specunen is not perfect. [The four proximal pieces increase rapidly 

 in size so that they are considerably larger than the others. iVll of 

 the actinal plates are granular.] There 

 appear to be one or two [there is but one 

 axillary] small disk plates between the 

 [basal adjoinmg infra] marginal and ad- 

 ambulacral plates just outside of the oral 

 angles. 



"Locality and formation. — To^vnship of 

 Grimsby [Ontario]; m the Niagara shale 

 [ = Rochester shale]. 



"Collector. — Johnson Pettit, Esq., fig. v.— theokkjinal figukeof me- 

 Grimsby." Tlie holotype is in the Vic- 

 toria Memorial Museum, Ottawa, Canada 

 (No. 2665). 



Remarlcs. — The holotype and only 

 kno^vn specunen of this species was seen 

 by the writer at Ottawa, and has now been freed from the rock so 

 that the abactinal side can also be studied. The generic charac- 

 ters are tliose of Mesoimlseaster and one is impressed at once by the 

 almost specific identity of the abactinal side of the specimen with 

 that of M. granti. However, as the specimens show sliglit diircr- 

 ences and come from different Siluric formations, it is thought best 

 to recognize them as distinct species. Moreover, the actinal side 

 of M. granti is still unlaiown. 



Abactinally aU of the skeletal pieces are of about the same size, 

 small, each ossicle irregular in outline, and more or less stellate. 

 Tliere are about 17 in the length of one-half inch. This skeleton is 

 more or less disturbed and it is impossible to clean olT all the adhermg 

 shale, so that it is difficult to make out the detailed arrangement. 

 The followi'.ig, however, can be made out: There is no true dislv as 

 in Petraster, and the parts that appear as such are either adliering 

 shale or displaced ossicles due to distortion during sedimentation. 



SOPAL^ASTER BELLULUS, AFTER BlL- 



LTOGS. Natural size. The speci- 

 men HAS STILL TOO MUCH SHALE 

 ADHERING TO IT AND BESIDES IS CON- 

 SIDERABLY DISTORTED, PREVENTING 

 ITS BEING SATISFACTORILY PHOTO- 

 GRAPHED. 



