NATITRAL SCIENCES OF PHILADELPHIA. 345 



clearly separated from Actinocrinvs (as properly restricted), to which genus 

 they have generally been referred ; but owing to the fact that at that time we 

 had never seen either a specimen or a figure of an Amphoracrinus showing the 

 arms, body, and parts connected with the opening of the vault, all preserved 

 together, we were under a misapprehension in regard to the true characters of 

 that group, and consequently placed Dorycrinus as a synonym under it. Re- 

 cently, however, we have been so fortunate as to see in Mr. Wachsmuth's ex- 

 tensive collection beautiful specimens of both types, in a remarkably fine state 

 of preservation, and from these we are satisfied that a systematic classification 

 of the Crinoidea requires these two groups to be separated as distinct genera. 



In the first place, it may be proper to remark that in both of these groups 

 the structure of the body, so far as regards the number and arrangement of 

 the pieces below the arm-bases, is almost exactly the same as in Actinocrinus.* 

 Tlie structure of the parts above, however, is very difi'erent. For instance, in 

 Dorycrinus the opening of the vault is never at the end of a more or less pro- 

 longed tube, or so-called proboscis, nor even in the slightest degree proboscidi- 

 form, but is merely a simple aperture penetrating a somewhat thickened pro- 

 tuberance, and nearly always situated and opening laterally. The vault in 

 this group is generally provided with a more or less prominent spine over each 

 ray, and a sixth one in the middle. Sometimes these are all, or in part, merely 

 represented by nodes, or even in some instances nearly obsolete, while in others 

 they are extravagantly developed. Again, Dorycrinus differs from both Acti- 

 nocrinus and Amphoracrinus in having, so far as yet known, always two arms 

 i-pringing directly from each arm-opening, and these arms always simple. Our at- 

 tention was first called to this by Mr. Wachsmuth, who is a vtry careful and 

 accurate observer, and we found it to be so in all the specimens in his collec- 

 tion, while he assures us that this is the casein all the specimens found by the 

 various collectors at Burlington, as well as all of those he has yet seen from 

 other localities, with the arms attached. Hence in all of the species of this 

 group described by Prof. Hall and others, where the number of arms has been 

 given from merely counting the arm-openings, — and specimens of these have 

 since been observed with the arms attached, — their number is found to he just 

 double that stated in the descriptions. It is also worthy of note that in this group 

 the body plates are either plane, more or less tumid, or tuberculiform, and 

 never marked with proper radiating costie, as we often see in Actinocrinus. 



The following is a list of the described species belonging to this group, all of 

 which are, so far as known, exclusively American types, and confined to the 

 Lower Carboniferous, viz. : Dorycrinus Ifississippiensis, Roemer, and D. Gouldi, 

 f D. cornigerus* D. divaricatus* D. trinodus, D. quinquelobus* D. symmetricus* 

 D. desiderattis, D. unispimis,* and D. subaculeati/s, Hall (sp.), all of which were 

 described by Prof. Hall under the name Actinocrinus. It likewise includes D. 

 Missouriensis* {==Act. Missouriensis, Shumard) and D. unicornis* [= Act. uni- 

 cornis,\ Owen and Shumard), as well as our D. subturbinatus,* originally de- 

 scribed as an Actinocrinus. 



It might at a first glance be supposed also to include Actinocrinus corniculus 

 and A. brevis of Hall, but these forms (which Mr. Wachsmuth's collections 

 clearly show to be only varieties of one species) have but a single arm from 

 each arm-opening (two to each ray), and these arms with the proportional 

 stoutness, general structure, and broad pieces at their bases, of Agaricorinus. 

 Hence this species can only be regarded as a somewhat aberrant form of the 

 latter genus. 



To the genus Dorycrinus we also refer the following new species : 



* Dorycrinus, however, differs from Actinocrinus in having the second radial pieces 

 nearly always short and quadrangular, instead of hexagonal. 



t Specimens of all the species 'marked witii an asterisk have been found with the arms 

 attached, and presenting the characters mentioned above. The arms of the others remain 

 unknown. 



X 'I'he proposed species A. iricornis and A. pendens, Hall, are believed to be only variedes 

 of unicornis of O. and S. 



1868.] 



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