34§ SMITHSONIAN INSTITUTION 



Protaxocrinus laevis (Billings) 

 Plate XLV, figs. 2-7 



Lecanocrinus laevis Billings, Rep. Geol. Surv. Canada, 1853-56 [1857], p. 278; Geol. Surv. Canada (Can. 



Organ. Remains), Decade IV, 1859, p. 47, pi. 4, fig. 30. 

 Taxocrimts laevis, Wachsmuth and Springer, Revision Palaeocrinoidea, pt. 3, 1886, pp. 144, 20J. — 



Springer, Jour. Geology, XIV, 1906, p. 487. 

 Protaxocrinus laevis, Springer, Geol. Surv. Canada, Mem. No. 15P, 1911, p. 11, pi. 3, figs. 10, 11a, b. 



In general form similar to P. elegans, but smaller and proportionally 

 shorter and broader, with evenly rounded instead of angular brachials, and 

 secundibrachs usually less than 5. Crown widest about the upper IIBr. A well- 

 preserved specimen of nearly maximum size has the following dimensions: 

 height of crown, 24 mm. ; of calyx at top of I Ax, 10 mm. ; width of calyx, 6 mm. ; 

 of base, 2.3 mm. In addition to the characters shown by P. elegans, we now 

 have those of the anal side. 



Posterior basal larger than others. RA of about the size, form and position 

 of RR in other rays. Anal tube large, with a series of large plates rising from 

 the right shoulder of the basal, suturally connected for some distance with the 

 right posterior ray but entirely free at the left side, where the margin of the left 

 posterior ray is smooth and rounded, and the large anal series is bordered by 

 smaller plates passing into perisome. Rays branching three times, then infold- 

 ing, with very long and slender finials coiling several times. Column about as 

 in P. elegans, sometimes tapering but little. 



Billings in describing this species noted its similarity to P. elegans, and relied solely on 

 the number of secundibrachs to separate them. This was plain enough in the type specimens, 

 which were all he had of each species. Of P. laevis, however, I now have eight additional 

 specimens, and they exhibit such variation in this character as to make it less definite than he 

 supposed, although the preponderance is toward the smaller number in conformity with the 

 generally shorter and broader habitus of the species. In 39 exposed rami of seven of these, 

 the number of IIBr is 2 in 1 ramus; 3 in 6; 4 in 19 ; 5 in 13. In the eighth (PI. XLV, 

 figs. 4a, b) there are 5 IIBr in 7 out of the 10 rami, and I was at first disposed to place it 

 under P. elegans on that account. But it wholly lacks the dorsal angularity of the lower 

 brachials, and even with its equal number of secundibrachs it is a shorter and broader form, 

 the measurements above given being taken from it. 



These two species are the earliest known Flexibilia. Neither of the types showed the 

 structure of the anal side, and their true characters have remained in doubt until recently, 

 when several excellent specimens of P. laevis came to light showing the anal structure to be 

 of the most primitive type. The close relation of these species to certain Inadunate forms 

 has already been pointed out. 



Besides the type I have figured five specimens of various sizes from three localities, 

 which show no material variation. 



Type. In the Victoria Memorial Museum of the Geological Survey of Canada, Ottawa. 

 The other specimens figured are in the author's collection. 



Horizon and locality. Ordovician, Trenton limestone ; Ottawa and Kirkfield, Canada. 



