ICHTIIYOCRINIDAE 3O7 



Schultze in 1867 (Mon. Echin. Eifler Kalkes, p. 38) described a species from the Middle 

 Devonian of the Eifel Mountains as Zeacrinus excavatus, and a variety as Z. interscapularis, 

 which clearly belong to this genus. Wachsmuth and Springer in 1879 (Rev. Pal, pt. 1, 

 p. 50) recognized their relation to the Flexibilia instead of to the Inadunata, but not being 

 then acquainted with Pacht's species or Ouenstedt's genus referred them without good reason 

 to Gnorimocrinus. 



Fraipoint in 1884 (Ann. Soc. Geol. Belgique, vol. 11, p. 112) described under the name 

 Zeacrinus beyrichi Dewalque a species of this genus from the Upper Devonian at Senzeille, 

 Belgium, and called attention to the resemblance of his species to the Zeacrinus interscapu- 

 laris and Z. excavatus of Schultze, from nearly equivalent strata in the Eifel Mountains ; and 

 he suggested that the three species presented characters sufficient to warrant their reference 

 to a new genus. 



Neither Pacht, Quenstedt, nor Von Zittel in their descriptions and discussions made any 

 mention of the infrabasals. Fraipoint says they are invisible in his specimen, and Rowley is 

 noncommittal, saying that they are " if present, hidden by the upper stem joint." This is not 

 strange, for these plates lie within a sharply bordered basal depression in which the top stem 

 joint is usually left firmly attached. Schultze found the second circlet of basals in the deeply 

 excavated basal cavity of his species, calling them " cryptobasalia," and erroneously stating 

 their number as five. 



Dactylocrinus represents a well-defined and vigorous type, with a wide geographical 

 range, having now been recognized from Devonian strata in Russia, Germany, Belgium and 

 America. 



All the European species are from the Middle or Upper Devonian ; those of the United 

 States are from the Hamilton, except the intermediate or doubtful species D. tardus from 

 the Waverly. 



The species, six in number, are arranged as follows : 



The Species of Dactylocrinus 



I. Ramules small, well-differentiated. 



Crown short, rotund, contracting upward. 

 Inner arm-trunks smaller than outer. 



Base deeply excavated, involving part of RR and all lower plates. 

 Ramules slender, at intervals of 4 to 6. 



iBr present or absent D. excavatus. 



Base broadly concave ; BB extending beyond cavity. 



Ramules small, at intervals of about 4 D. concavus. 



Crown elongate, spreading upward. 

 Main arm trunks about equal. 

 Base shallowly concave. 



Ramules slender, at intervals of about 3 D. oligoptilus. 



Base sharply excavated. 



Ramules stout, at intervals of 1 D. beyrichi. 



II. Ramules large, resembling arm divisions. 



Crown elongate. Base shallowly concave. 

 IIBr 3. 



Ramules at intervals of 4 or 5 D. alpena. 



IIBr 4 or 5. 



Ramules at intervals of 6 or 7, approaching dichotomy D. tardus. 



