TAXOCRIN IDAE 349 



Protaxocrinus girardeau n. sp. 

 Plate XLV, fig. 8 



A small species, having the habitus of P. laevis, from which it differs by 

 only slight modifications. The calyx and arms are rather more slender, basals 

 and brachials more elongate than in the typical form of that species, and it re- 

 sembles the exceptional cases rather than the type in having mostly five IIBr. 

 iBr few and small (perhaps only one) followed by perisome. Anal tube narrow 

 and delicate. The column is exactly like that of P. elegans. Dimensions of 

 largest specimen: height of crown, 17 mm.; of calyx at top of I Ax, 9 mm.; 

 width of calyx, 5 mm. ; of base, 25 mm. 



When this species was proposed the specimen figured on Plate XLV, from the Girardeau 

 limestone at Thebes, Illinois, was the only one known; since that time, and too late for 

 figuring, a second specimen has been found from the same horizon in Missouri, which is in 

 every way confirmatory of the type. The very close affinity of this Silurian form with the 

 primitive species of the Trenton affords a striking illustration of the reappearance of types in 

 these rocks after a long geological interval. The fact is well recognized that many scarcely 

 distinguishable descendants of Trenton species which are entirely absent in the Cincinnatian 

 appear in the succeeding formations, and that in the Richmond and Girardeau beds there is 

 a recurrence of faunas consisting of species which find their nearest relatives, not in the 

 immediately antecedent Maysville or Lorraine, but among the typical Trenton faunas. 



Type. In the author's collection. 



Horizon and locality. Silurian, Girardeau limestone ; Thebes, Illinois, and Cape 

 Girardeau, Missouri. 



Protaxocrinus robustus n. sp. 



Plate XLV, figs, p-u 



A robust species, with heavy arms 'tapering but little. Base expanding 

 rather suddenly from column facet. Arms broadly and deeply rounded. Crown 

 widest about IIBr 3 , where height to width is about 1.8 to 1 ; calyx at top of IAx, 

 1.1 to 1 ; spread from base, 1 to 3. Height of crown of maximum specimen, 21 

 mm. ; width, 12 mm. Surface smooth. 



IBB low, often not exposed beyond the column. IBr increasing in width 

 upward. IIBr 3, without exception in three specimens. Lower Br with straight 

 sutures, becoming slightly arcuate distally. iBr few and small. RA mucb 

 smaller than RR in other rays. Anal series slender, not adhering to right pos- 

 terior ray. Column facet as large as infrabasal ring. 



This Niagaran representative of the genus shows a constant difference from the Ordo- 

 vician species in the lower IBB, and shorter, heavier rays. Three specimens of it were found 

 at the same locality in Tennessee showing little variation ; one of them, though small, being 

 in very perfect condition. In the short, robust habitus this species is very close to P. ovalis 

 of Gotland. 



Types. In the author's collection. 



Horizon and locality. Silurian, Niagaran Group, Brownsport limestone, Beech River 

 formation ; near Decaturville, Tennessee. 



