148 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



width at base of the rays nearly equal and less than the width of the 

 disk. The upper surface is covered with crowded irregularly polyg- 

 onal tumid plates. Madreporiform tubercle very large (1J lines in 

 diameter), irregularly porous, and rugged with branching vermicular 

 ridges, excentric toward base of the two posterior rays. Ambulacral 

 groove very narrow, bordered with a row of large transversely oblong 

 adambulacral plates, wider than long, about 6 in 2 lines at middle 

 of ray; margin of the rays bordered with a rather smaller row of 

 similar marginal plates; between the row of adambulacral and mar- 

 ginal plates an intercalary row of small irregular plates. Width of 

 disk between the rays, 7 lines; from tip to tip of rays, about 1 inch 2 

 lines; length of ray, about 5 lines. 



" Very rare in the fine sandy Upper Silurian rocks of Moonee Ponds, 

 Flemington, a little north of Melbourne [Australia]. ' ' 



Remarks. The holotype exposes the abactinal side, but the plates 

 of two of the rays are absent, exposing the actinal skeleton, which is 

 therefore seen from its inner side. So far as one can judge of the 

 description and illustration, the species is a small but genuine Petras- 

 ter. Abactinally the rays have conspicuous radial and supramar- 

 ginal columns, each with about 17 ossicles, that are tumid and are 

 all closely adjoining. Outside of these in the distal portion of the 

 rays are the equally conspicuous inframarginals, and they margin 

 not only these parts but the entire animal; proximally the inframar- 

 ginals separate more and more from the supramarginals, forming 

 small ambital areas, occupied by a number (can not be determined) 

 of rounded plates that now appear not to have been closely adjoining. 



Madreporite large, radiately striate, situated in an interradius and 

 well inside the ambital area. 



Ambulacralia large, about 12 in a column, and opposite one another. 

 Adambulacrals smaller, about 14 in a column. Interbrachial struc- 

 ture unknown. 



Genus LINDSTROMASTER Gregory. 



Lindstromaster GREGORY, Geol. Mag., dec. 4, vol. 6, 1899, pp. 344, 346. 

 Hisingeraster STURTZ, Verh. naturh. Ver. preuss. Rheinl., etc., vol. 56, 1900, 

 pp. 224, 225 (same genoholotype as for Lindstromaster). 



Original description. "Palseasterinidae with flat pentagonal disk 

 and five short blunt rays. 



''The plates of the disk are large, polygonal, tuberculate, and 

 crowded into a close tessellate pavement, which completely covers 

 the interradial areas. 



