TAXOCRINIDAE 4O3 



down within the infrabasals. The structures can be well studied in the diagram, 11c, where 

 the old plates are shaded and the new growth shown in outline. 



Recuperation of more than a single ray in Paleozoic crinoids has not hitherto been 

 recorded, but I am now able to report an interesting case of apparently habitual detachment 

 of all the arms in life, and occasional regeneration, in the rather abundant species of the 

 Cincinnati area described as Heterocrinus juvenis Hall (24th Report New York State Mus., 

 1872, pi. 5, figs. 9, 10; Meek in Palaeontology of Ohio, vol. 1, pi. 1, figs. 3a, b). The species 

 is usually found in good preservation, except that by far the greater number of speci- 

 mens are minus the arms, as shown in Hall's figures 9 and 10 and Meek's figure 3, above 

 cited. The break is almost invariably at the level of the tegmen, just above the first primi- 

 brach, and it includes the anal tube as well as the arms. This loss of the normal food- 

 gathering apparatus was not immediately fatal, for in a large number of individuals the 

 fractures were partially repaired, leaving the surfaces smoothly rounded ; and the stumps 

 of rays are often bent inward as if trying to close over the tegmen, as shown in Hall's figures. 

 Efforts at recuperation were made, sometimes producing a new set of arms, usually of a 

 different size or color and more or less imperfect, and sometimes resulting only in the addi- 

 tion of a few dwarfed brachials. 



This tendency to cast off the arms resulted in a remarkable dwarfing of the crown, which 

 is usually no larger in diameter than the stem, while the latter, as compared with the stem of 

 crinoids generally, appears relatively of enormous size. Among 195 specimens of this 

 species in the collection before me 117 have lost their arms, leaving the fractured surfaces 

 rounded, while 55 show more or less recuperation. Specimens with the arms in the normal 

 condition, like Meek's figure 3a, are quite rare. 



Similar occurrences are frequent among the Recent Bourgueticrinidae. Danielson ' has 

 described some of them in the Arctic species, Bathycrinus (Ilycrinus) carpenteri, and Doeder- 

 lein " in species of Bathycrinus and Rhizocrinus. The species of these genera in which the 

 loss and occasional regeneration of arms are chiefly observed all have the relatively very 

 large stem and diminished crown seen in the fossil species above mentioned ; and, as in that 

 species, the separation of the arms seems to be a very common occurrence, leading to the 

 suggestion by both these authors that it may have been a voluntary autotomy. Some of the 

 instances of regeneration are very remarkable — one reported by Doederlein (Siboga, p. 6, 

 pi. 5, fig. 3) being that of a stem which had lost the entire crown, but still had life enough to 

 regenerate structures at the proximal end, which took the form not of calyx plates, but of 

 radical cirri, thus producing the singular arrangement of a stem with a root at each end. 



Types. The original of White's description cannot be found. The other specimens 

 figured herein are in the author's collection. 



Horizon and locality. Keokuk division of the Lower Carboniferous. Abundant at 

 Crawf ordsville, Indiana ; a few specimens have been found at Indian Creek in the same 

 county at a horizon a little lower than the beds at Crawfordsville. This is one of the very 

 few species which is found in both the Crawfordsville and Indian Creek beds ; it seems to 

 have begun in the latter, where it is rare, and culminated in the former. 



1 Norwegian North-Atlantic Expedition, 1892, pp. 10-12, pis. 1, 3. 



2 Gestielten Crinoiden der Siboga-Expedition, 1907, pp. 6-18, pis. 1-8; Deutsch Tiefsee-Expedition, 

 1912, pis. 3, 4, 5, 6. 



