3°4 



SMITHSONIAN INSTITUTION 



DACTYLOCRINUS Quenstedt 



Plate XLI 



Dactylocrinus Quenstedt, Petref. Deutschlands, IV, 1876, p. 520. — Von Zittel, Handbuch Palaeontologie, 

 1879, p. 354. — Wachsmuth and Springer, Revision Palaeocrinoidea, pt. 3, 1886, p. 233. — Jaekel, 

 Zeitschr. d. Deutsch. geol. Gesell. for 1897 [1898], p. 45. — Bather, Treatise on Zoology (Lankester), 

 pt. 3, 1900, p. 189. — Springer, Amer. Geologist, XXX, 1902, p. 95; Jour. Geology, XIV, 1906, 

 p. 518. — Zittel-Eastman, Textbook Paleontology, 191 3, p. 205. 



Dimerocrinites, Pacht (not Phillips), Verhandl. K. Russ. Min. Gesell., 1853, p. 339 (Separate 1852, p. 8). 



Zeacrinus (Troost), Schultze (not Hall), Mon. Echinodermen Eifler Kalkes, 1867, p. 38. — Dewalque in 

 Fraipont, Ann. Soc. Geol. Belgique, XI, 1884, p. 112. 



Aristocrinus Rowley, Amer. Geologist, XVI, 1895, p. 217. 



Callawaycrinus Rowley, Amer. Geologist, XVI, 1895, p. 219. 



Not Dactylocrinus Sladen, Proc. Geol. and Polyt. Soc. West Riding, Yorkshire, 1878 (The genus 

 Poteriocrinus and allied forms), p. 4. 



^0© 



Fig. 40. Dactylocrinus 



Ichthyocrinidae with rays above radials separated in lower part. Crown 

 elongate to rotund, spreading from radials up. Infrabasals entirely within 

 ring of basals. Posterior basal elongate. Radianal not identifiable. Anal x 

 followed by smaller plates in one or more series. Interbrachials few; areas 

 narrow, with rays meeting above them but not interlocking. Primibr'achs two. 

 Arms heterotomous; rays in twenty main trunks with ramules on inside of 

 dichotom, usually simple. Column large, enlarging proximally. 



Genotype. Dimerocrinites oligoptilus Pacht. 



Distribution. Devonian and base of Lower Carboniferous; Russia, Ger- 

 many, Belgium, and the United States. 



This genus marks the introduction of the heterotomous arm, so far as we know, in the 

 family Ichthyocrinidae. In most of the species it is a very regular mode of. branching, with 

 symmetrical ramules, small, close together and gradually diminishing, being but a short step 

 from pinnulation although only unilateral. The shortest intervals are in D. beyrichi from 

 the Rhineland Devonian, in which the ramules are borne on every second brachial, that is 



