EEVISION OF PALEOZOIC STELLEROIDEA. 



220 



imperfect, being merely an incomplete disk, and tlie inner ends of tlie 

 rays. It does not conform to the characters of Protaster given in 

 Prof. Forbes's diagnosis, in all respects, since its disk, especially on 

 the upper side, is covered by an integument composed of a vast 

 number of very minute grains of calcareous matter, instead of dis- 

 tinct imbricating scales. It is therefore not improbable that perfect 

 specimens would show other characters that would warrant the 

 establishment of a new genus or subgenus for such forms, in which 

 case the name Alepidaster might be applied to the group." 



GenoTiolotype . — Protaster {?) gr^anuliferus Meek. 



Original description of 

 Protasterina. — ' ' Rays five, 

 slender, flexible, and ex- 

 tending much beyond a cir- 

 cular and minutely granu- 

 lar disk, which is provided 

 with short, slender, and 

 outwardly directed spines; 

 inner ray pieces [ambu- 

 lacra] regularly alternating, 

 of an hour-glass shape, and 

 interlocking along the me- 

 dian line, which is there- 

 fore not straight but zig- 

 zag; outer ray pieces elon- 

 gated [adambulacrals or 

 side plates], directed ob- 

 liquely outwards, so as to 

 partly overlap each other; 

 two rows of large pores between the mner [ambulacral] and outer 

 [side plates] ray pieces; in the type-species these pores appear to have 

 been occupied by loosely-fitting subpyramidal plates, some of which 

 have a deep depression in the top, as though they were perforated; 

 their true nature, however, is very uncertain. Oral pieces ten, each 

 pair bemg formed by two of the outer ray pieces. Type, P. Jiinhriata." 



When the original material of Alepidaster and Protasterina is re- 

 studied, it may be showTi that the latter is not a synonym of the 

 former, but at present the wi'iter does not see any generic differences. 



Alepidaster is easily distmguished from Protaster, not only by its 

 greater geologic age, but also in that its disk is minutely granular 

 and spiniferous while that of the latter is scale-bearmg. Further, 

 when the exact shape of the ambulacrals is determined, it is probable 

 that other differences wall be found there. Particular attention 

 should be paid to Ulrich's statement that in Protasterina the podial 

 openmgs "appear to have been occupied by loosely fittmg, sub- 



FiG. 26.— Diagrams of Alepidaster granuliferus (Meek). 

 Drawn by E. O. Ulricii from a specimen in the United 

 States National Museum. A, Actinal view of ray 

 plates. B, Same from abactinal side. C, Section 



THROUGH ray. D, SiDE-PLATE FROM THE INSIDE AND IN 



SECTION. 



