NATURAL SCIENCES OF PHILADELPHIA. 153 



This species is related to Potcriocrbws hursxformis, of White, which has its 

 body formed exactly as in Foteriocrinus, with its arms and primary radials pre- 

 senting all the characters of Zeacrhnis, as was noticed by Dr. White ; thus 

 showing, with the species under consideration and some others, that Zeacnnus 

 can scarcely be regarded as more than a subgenus under Poteriocrinites. The 

 form that we have here described diifers, however, specifically from Dr. White's 

 species, in having its body proportionally shorter and smaller. Its arms also 

 differ in being very distinctly rounded instead of fiat, while its anterior ray 

 supports two arras directly on the second radial piece, as in all the other rays, 

 instead of having the first bifurcation in that ray on the fourth piece. 



The specimens are not in a condition to show much of the ventral prolonga- 

 tion, but one of them shows that it is very nearly as long as the arms, and 

 somewhat expanded and crowned with short spines at the upper extremity. 



Locality and position. Upper division of the Burlington group, at Burlington, 

 Iowa. Lower Carboniferous. No. 319 of Mr. Wachsmuth's collection. 



Genus ACTINOCRINITES, Miller. 



In the second volume of the Illinois Reports, published in 1866, after admit- 

 ting as distinct genera from Aciinocrinites the groups 3Iegistocrinus, Agaricocri- 

 nus, Amphoracrinus and some others, we also separated under the name Stroto- 

 crinus a group of remarkable American Carboniferous species, of which Acti- 

 nocr. perumbrosun, 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. vmtricosus, Hall, 

 may be regarded as an example. We readily observed that while in some of 

 their characters they agree most nearly with Slrotocrimis, 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 pro- 

 visionally as a section under Aciinocrinites. 



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 Actinocrinit€s,^lhvii it should be 

 placed as a distinct subgenus under the former. Adopting this view, and ad- 

 mitting, as we have elsewhere done, that the Batocrimts and Dorgcrinus groups 

 should stand as distinct genera, the genus Actinocrinites vtoxxlA be left to include 

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

 and A. polydactylus, and de Koninck's A. slellaris, A. diversiis, A. deornatus and 

 A. armatiis, with various others ; and the group including A. inullihraehiatus 

 and its allies. 



The typical forms of Aciinocrinites, which agree almost exactly with all the 

 other genera mentioned, as well as with the A. muUibrachiatus group, in the 

 number and arrangement of the pieces composing the walls of the body below 

 the bifurcations of the rays, are distinguished by the following characters, 

 never found all combined in any one of the other groups : 



In the first place, they have the arm bases, or brachial pieces, and adjacent 

 parts (sometimes as far in as the third primary radials) grouped together so as 

 to form five more or less protuberant 1 obes,f and so far as yet known to us, at 



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



opportunity to study. 



t Since these remarks were in type, we observe, on consulting Miller's Nat. Hist, of the 

 Crinoidea, to which we had not previously had access for many years past, that he seems 

 to have confounded two very distinct forms under the one name of his typical species, 

 Actinocrinites triacontadactylus. One of these, if correctly ie2>resented on plati I of his work, 



1869.] 



