364 PROOBEDINGS OP THE ACADEMY OF [1881. 



We propose for this little group, which is one of the oldest of 

 the known Crinoids, the name '■'■ Archseocrinus " and make Billings' 

 Gli/piocrtjius lacunosus the type of the genus. 



Generic Diagnosis. — Calj^x large, pear-shaped, sometimes 

 obcjonical ; plates smooth or granulated ; the radial plates with 

 keel-like elevations along their median line, but less prominently 

 than in Glyptocrinus, and the earinse narrower. 



Fnderbasals five, pentagonal, rather small and rarely extending 

 beyond the column. Basals five, hexagonal, with a truncate upper 

 side, supporting the first radial plates. Primary radials 3 X 5, of 

 medium size, gradually decreasing upward, width and height 

 about equal. They support two rows of secondary radials of three 

 to four plates in each row, which are followed in the same line by 

 the arm plates, all further divisions of the rays taking place in 

 the arms. The ra3'S are widely separated by large interradial 

 areae. Arms short, slender, the branches divergent ; composed 

 of two rows of cuneiform pieces, alternately arranged and inter- 

 locking. Interradial areas large ; resting directly upon the upper 

 truncate side of the basals, and passing gradually into vault 

 pieces. The plates of the two proximal series are generally of 

 equal size, all succeeding ones are much smaller. There are two 

 plates in the second series in all five areas, those at the posterior 

 side are probably a little wider. Interaxillaries represented by 

 one or more plates. 



Vault and anus unknown. Column round. 



Geological Position^ etc. — Archseocrinus is onl}-^ known from 

 the Lower Silurian of America. 



We place here the following species : — 



*1857. ArohsBocrinus lacunosus Billings. Type of the genus. (Glyptoor. lacunosus) 



Geol. Rep. Canada (Rep of Progress), p. 261; Ibid., 1859, Decade iv, p. 61, 



PI. 8, figs. 3 a-e. Trenton limest. Ottawa, Canada. 

 *1857. Archaeocr. marginatus Billings. (Glyptocr. marginatus) Geol. Rep. Canada. 



(Rep. of Progress), p. 260; lb., 1858, Decade iv, p. 69, PI. 9, figs. 1, 1 a. 



Trenton liraest. Ottawa, Canada. 

 *1857. Archaeocr, miorobasilis Billings, (Thysanocr. — Bhodocr. — microbasilis) 



Geol. Rep. Canada (Rep. of Progress), p. 264; Ibid., 1859, Decade iv, p. 63, 



PI. 6, fig. 2. Trenton limest. Ottawa, Canada. 

 •••1857. Archaeocr, pyriformis Billings. (Thysanocr.— Rhodoor.— pyriformis) Geol. 



Rep, Canada (Rep. of Progress), p. 262 ; Ibid., 1869, Decade iv, p, 61, PI, 6, 



figs, 1 a-d. Trenton limest, Montreal, Canada. 



