REVISION OF PALEOZOIC STELLEEOIDEA. 177 



Stenaster pulclieUus Billings and this is the general consensus of opinion. 

 The WTiter unfortunately had no material of the genotype of Uras- 

 terella for study. However, since U. grandis is closely related to U. 

 jmlcJieUa and shows so much more detail, it is here accepted as the 

 genotype for the time being. 



Professor Hall (1870) wrote: "In Stenaster = Urasterella, however, 

 we have the absence of adambulacral plates." This is nevertheless 

 not the case, for the coin-shaped marginal series in S. pulchellus are 

 the ambulacral plates, since wcU-developed inframarginal plates, as 

 in Palseaster, are absent in mature Urasterella. The inframarginals 

 are, however, seen to be present in U. pulchella or in the distal ends 

 of the rays in other species, though proximally they are so modified 

 as not to be readily distinguishable from the ambital plates. In the 

 axils of the young of U. ulrichi the inframarginals are weU developed, 

 along with single mterbrachial margmal plates, but in mature speci- 

 mens of other species none have been seen. 



Of Roemeraster the writer has seen tln-ee excellent specimens skil- 

 fully prepared by Stiirtz which clearly show that this genus has the 

 generic structure of Urasterella. Stiirtz ^ describes this genus as 

 having '^ strong marginal plates" inside of the "small, cornered adam- 

 bulacrals." Our sjDccimens do not show such plates, and if present 

 they can not be adambulacrals. This fact can be demonstrated 

 . in a weU-preserved distal end of a ray, where two columns are present 

 on each side of the ambulacrals. The innermost column of closely 

 adjoinmg plates increase in size, retain theii* position beside the ambu- 

 lacrals, and become the most prominent of the entire animal, while 

 the outermost column soon change in aspect, the plates become 

 separated and assume the characters of the ambitai pieces. This 

 is Ukemse true in the young of U. ulrichi where the axillary areas 

 also have distinct mterbrachial marginal and two larger proximal 

 inframarginal plates. Passing distally, the latter also soon change 

 their form, are separated one from another and are not distinguish- 

 able from the ambital plates. vStiirtz further describes and figures 

 five mterbrachial ossicles in mature Urasterella aspenda which are 

 also well developed in the young of U. ulrichi. Urasterella is an 

 easily recognized genus and the triangular ambital plates drawn out 

 into short blunt erect rods are pecuhar to it, a character again re- 

 peated in Roemeraster. Under these circumstances the latter appears 

 to be mdistinguishablo from Urasterella. For other remarks sec 

 U. asperula. On the other hand, Gregory regards Roemeraster as a 

 good genus and places it erroneously among the ophiuricUike asterids 

 in the family Taeniasteridae. 



> Verb, iiaturh. Ver. preuss. Rheinl., etc., vol. 50, 1893, p. 52. 



