NO. 3 ON THE FOSSIL CRINOID FAMILY CATILLOCRINIDAE 21 



zvachsmuthi with 34-38 arms to C. tennesseeae with 51-57 arms (Pal. 

 Deutschl. 1895, p. 44). Wanner has pointed out (Perm. Echin. i, 

 1916, p. 7) that the succession does not hold good for the Permian 

 forms, in which the number of arms is reduced to 13-20. Jaekel's 

 theory also falls when tested by the facts relating to the species of 

 Catillocrinus. For C. tennesseeae, the species with the greatest num- 

 ber of arms, instead of being the last in the geological series, as then 

 supposed and so listed in the works of that time, is the earliest ; and 

 the modification in number of arms in geological succession proceeds 

 in exactly the reverse of what he assumed — diminishing from 35-58 

 in C. tennesseeae of the earliest Lower Carboniferous, to 13-20 in 

 C. carpenteri of the latest member. Thus the end of the series in 

 the American rocks is marked by a retrogression, finishing in the 

 Chester (Kaskaskia) with a degenerate species, the smallest of all, 

 ranging from 2.5 to 4.5 mm. diameter, and represented by a number 

 of specimens from three distinct localities. 



With our present knowledge of the different occurrences of this 

 type, it seems evident that the number of arms is largely a matter 

 of size, both as between the different species, and among individuals 

 within the same species. And the two characters taken together 

 form an excellent means of dififerentiating the species in the suc- 

 cessive geological formations. In C. bradleyi, however, the arms are 

 more slender than in any other species, and their number, in propor- 

 tion to size of calyx, is greatly increased. 



Catillocrinus tennesseeae, the earliest, is also the largest known 

 species, ranging in our collections from 18 to 27 mm. (exceptionally 

 13) longer diameter of the elliptic dorsal cup, measured at the upper 

 edge; and the number of arms increases correspondingly from 43 

 (exceptionally 36) to 58. The closely allied C. turbinatus, from the 

 same formation, has a calyx of 11 to 21 mm., with 37 to 53 arms. 

 In the next succeeding species, C. wachsmuthi of the Upper Burling- 

 ton limestone, the size diminished to 6-12 mm., and the corresponding 

 number of arms to 24-39. It was followed by the new species, C. 

 shumardi in the Keokuk, a still smaller species with diameter of 4-6 

 mm., and arms 20-25. Next came C. bradleyi from a higher horizon 

 of the Keokuk, a species of more vigorous growth but smaller arms, 

 ranging from 6.5-8 mm. diameter with 40-46 arms. Finally, in the 

 latest member of the Lower Carboniferous, the Chester (Kaskaskia), 

 we have the end of a retrogressive series, in which the size is re- 

 duced to 2.5-4.5 mm. diameter, and the accompanying number of 

 arms to 13-24. There is a sufficient number of specimens to prove 



