66 



BULLETIN 



UNITED STATES NATIONAL MUSEUM. 



l2 



From the two excellent illustrations the following is made out: 

 Inframarginals conspicuous and as large as the adambulacrals. 

 Both columns finely tuberculate, with the ossicles of each alternating 

 with one another. Proximally the inframarginals of adjacent rays 

 rest on a somewhat larger axillary plate. The interbrachial areas 

 are therefore made up of single axillary ossicles (Jaekel's marginal 

 oral) and in front of these lies a pair of pointed adambulacrals, the 

 conspicuous pieces of the oral armature. These are perforated for 

 the continuation of the ring canal. The podial openings as usual 

 lie in the corners of four adjacent adambulacrals and ambulacrals, 



but there is a de- 

 cided tendency to 

 restrict them to 

 only one of the am- 

 bulacral corners. 



Abactinal area 

 unknown. 



Remarks. This 

 genus appears to be 

 closely related to 

 Hudsonaster, but 



FIG. 6.-SILT7RASTER PERFECTUS (JAEKEL'S FIGURE 3). Oj TO Og, AMBU- , -1 o, -7 , 



LACRALIA OF ONE SIDE; ABOVE THESE ddi TO ddg, THE ADAMBULACRALIA, l l6 ' 1 



adi AS MOUTH CORNER PIECE; dfg, PODIAL GROOVES; dpff, PODIAL OPEN- DlOrC fully WOrked 



INGS; m, INFRAMARGINALIA; mo, THE SINGLE AXILLARY INFRAMARGINAL; , , n 



RC, RING-CANAL IN MOUTH CORNER PLATES. Ut lt} ^ ^maUl aS 



an obscure genus. 



Genoholotype and only species. S. perfectus Jaekel. Ordovicic 

 (D4), Zahorzan, Bohemia. 



Family PAL^ASTERID^E Gregory (emend.). 



Palaeasteridae (part) MILLER, N. Amer. Geol. Pal., 1889, p. 216. GREGORY, Geol 

 Mag., dec. 4, vol. 6, 1899, p. 344 (contains Palseasterinae, Xenasterinse, and 

 Lindstromasterinse); Treat. Zool., vol. 3, Echinoderma, 1900, p. 250. 



Palsecisterinas SCHONDORF, Jahrb. nassauisch. Ver. Naturk., Wiesbaden, vol. 63, 

 1910, p. 244. 



Palxgoniasteridx (part) STURTZ, Palaeontographica, vol. 36, 1890, p. 246 (contains 

 Aspidosomella and Pal&aster). 



Primitive, derived, five-rayed Phanerozonia with the ambulacrals 

 slightly alternate or opposite. Interbrachial arcs incipient or some- 

 what enlarged, and occupied by single axillary marginal plates. No 

 accessory interbrachial or axillary interbrachial plates present, but 

 there are developed accessory abactinal ray ossicles. Actinal plates 

 consisting of ambulacrals, adambulacrals, and inframarginals. Mad- 

 reporite abactinal. 



Contains : 



Palseaster Hall. 

 Australaster, new genus. 



