PALJEOZOIC FOSSILS. 287 



Pal^ ASTER (Argaster) antiqua (Troost). 



PLATE 



jlsterias antiqua : Troost, Trans. Geol. Soc. of Pennsylvania, Vol. i, pa. 232, pi. x, 



f. 9. 1835. 



Petratter (?) antiqua : Tboost, Shumakd, Catalogue of Palaeozoic Fossils, etc., 



p. 386, 1865. 



Body of medium size, five-rayed; rays flexuose. Marginal range of plates 

 large, somewhat quadrangular, with their outer faces subnodose : the 

 basal plates of the series single, broadly triangular, with slightly trun- 

 cated lateral angles ; the obtuse angle of the plate directed towards the 

 axil of the rays. This form of the basal plate leaves, at the base of the 

 marginal ranges and bordered by the adambulacral ranges, a small trian- 

 gular space which is filled by small plates or granules ; a character not 

 observed in any other species of this genus. 

 Adambulacral ranges composed of small plates, which are nearly twice 

 as numerous as those of the marginal range ; the basal plates of the 

 ranges are elongate, triangular, in pairs from the adjacent rays. Ambula- 

 cral grooves occupied by a single row of subquadrate ossicula, which extend 

 across and alternate with the adambulacral plates of each margin : the 

 pores have not been observed. 

 Upper or dorsal surfaces not known, except from a few small plates out- 

 side of the marginal plates, which appear to have been crowded over 

 by pressure. (Perhaps these latter plates may have formed a slight dise 

 between the rays.) 



The specimen is so imperfect that it is not possible to give a full descrip- 

 tion of parts ; the outer limits of the rays having been obscured by scraping 

 and the too free use of acids, before the specimen came under my observa- 

 tion, so that the exact number of marginal and other plates cannot be 

 determined. This form differs, however, from all others described or known, 

 in the comparatively large marginal plates, the triangular spaces at the 

 base of the marginal ranges, and the single series of ambulacral ossicula. 

 It is possible that this last character may prove to be of generic impor- 

 tance, could we obtain specimens sufficiently well preserved to show these 

 and other characters in a more perfect manner. 



Geological formation and locality. The specimen is from the Hudson- 

 river group, Harpeth river, Davidson county, Tennessee. 



PaL^ ASTER EUCHARIS (n. S.). 

 PLATE IX, FIGS. 3, 3*, 3a & 4. 



Body rather large ; the largest individual being one inch and seven-eighths 

 from the centre of the body to the extremities of the rays ; the whole 

 having a robust aspect : rays acutely pointed at the extremity. Upper 



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