FOSSILS OF THE BURLINGTON UKOUP. 339 



sea until they found a suitable station to attach themselves, where they 

 remained during- life. May they not, therefore, have been attracted to 

 the bodies of Crinoids by the numerous little organisms brought in by 

 the action of cilia, along the ambulacral furrows of the arms of the 

 Crinoids, or in currents produced by the motions of the arms of the 

 latter? The excrementitious matter of the Crinoid could doubtless 

 have passed out under the foot of the Platyceras, supposing the opening 

 in the Crinoid sometimes covered by these shells to have been the anus ; 

 but it is difficult to conceive how food could have passed in, if we sup- 

 pose this opening to be the mouth. 



GENUS ACTIXOCRINTrES, Miller. 



(Proceed. A cad, Nat. Sci., Philad., 1869, p. 153.) 



In the second volume of the Illinois reports, published in 1866, after 

 admitting as distinct genera, from Actinocrinites the groups Megistocrinw, 

 Agaricocrinus, Amplioracrinus and some others, we also separated under 

 the name Strotocrinus a group of remarkable American Carboniferous 

 species, of which Actinocrinus penimbrosus, Hall, was regarded as the 

 type. At the same time that we made this separation there were 

 amongst the collections before us specimens of another allied type, in 

 regard to the proper disposition of which we were in considerable doubt. 

 These belong to the group of which A. ventricosus, Hall, may be re- 

 garded as an example. "We readily observed that while in some of 

 their characters they agree most nearly with Strotocrinus, that in others 

 they seemed to be more closely allied to Actinocrinites, and at one time 

 we were very much inclined to the opinion that a strictly systematic 

 definition of all the different genera of the Crinoidea would require 

 their separation as a distinct intermediate genus. Wishing to avoid 

 disturbing the existing nomenclature, however, as much as possible, we 

 finally concluded to place this group provisionally as a section under 

 Actinocrinites. 



Since that time we have had an opportunity to study an extensive 

 series of these and the allied groups, in Mr. WACHSMUTH'S collection, 

 and have been led to the conclusion that if this type does not form a 

 separate genus, holding an intermediate position between Strotocrinus 

 and Actinocrhntrx, that it should be placed as a distinct sub-genus 

 under the former. Adopting this view, and admitting, as we have else- 

 where done, that the Batocrinus and Dorycrin-us groups should stand as 

 distinct genera, the genus Actinocrinites would be left to include two 

 sections ; * that is, the typical forms, such as Miller's A. triacontadac- 



* There are doubtless other sections, but we allude here to the forms we have had an opportunity to 

 itndy. 



