1881.] NATURAL SCIENCES OF PHILADELPHIA. 283 



187S. Desmidocr. macrodactylus Angel. leonogr. Grin. Suec, p. 5, PI. 16, figs. 20, 



21. Upper Silur. Gothland, Sweden. 

 1S7S. Desmidocr. pentadactylus Angel. leonogr. Crin. Suec., p. 5, PI. 16, figs. 



15, 22. Upper Silur. Gothland, Sweden. 

 1S7S. Desmidocr. tridactylus Angel. leonogr. Crin. Suec, p. 5, PI. 16, figs. 4, 4 a. 



Gothland, Sweden. (Probably identical with D. macrodaetylns.) 



6. AGAEICOCRINUS Troost. 



1850. Troost. List. Crin. Tenn. (Proc. Amer. Association), 



1858. Hall (Subgenus of Actinocr.). Geol. Rep. Iowa, i, Pt. ii, p. 560. 



1866. Shumard (Subg. of Actinocr.). Cat. Pal. Foss., Pt. i, p. 350. 



1873. Meek and Worthen. Geol. Rep. 111., v, p 397. 



1878. Wachsm. and Spr. Proc. Acad. Nat. Sci. Pbila., p. 350. 



Syn. Amphoracrinus Roemer (not Austin), 1855. Letb. Geogn. 

 (Ausg. 3), p. 250. 



Syn. Amphoraci'inus Hall (not Austin), 1861. Bost. Jour. Nat. 

 Hist., p., 280. 



Syn. Actinocrinua Hall (in part), 1858. Geol. Rep. Iowa, i, Pt. ii. 



Some authors haA'e confounded Agaricocrinus with Amphora- 

 crinus Austin, with which it agrees in the depressed form of the 

 cal3-x and in the elevated dome, but while in Agaricocrinus the 

 calj'x or its equivalent extends to the secondary radials, that of 

 Amphoracrinus is properl}' composed of few plates, all the upper 

 radials, from the third primary up, being parts of free rays. 

 Amphoracrinus differs also in the form of the dome, in the spini- 

 ferous proximal vault pieces, in having an anal tube, in the surface 

 ornamentation, and in the arms. 



Hall, who first defined Troost's genus Agaricocrinus.^ placed it 

 subgenerically under ActinoaHnus, and referred to it exclusively 

 species with a broadl}' truncate or concave dorsal side, leaving all 

 similar t3'pes with a convex calyx under Actinocrinus. This can- 

 not be sustained, as we find among the species of this group all 

 intermediate gradations in this feature, while at the same time they 

 agree most remarkably in all other important characters. The 

 structure of Agaricocrinus is so marked that we do not hesitate 

 to rank it as a distinct genus. The differences in the form of the 

 calyx are modifications in geological succession. Species with 

 convex sides are confined to the Waverl}' group and to the Bur- 

 lington limestone ; species from the Upper Burlington are truncate 

 below, or slightly convex, rarely concave ; while the Keokuk 

 species, without exception, are deeply concave in the basal regions. 



We place under Agaricocrinus^ subgenericall}", AlloprosaUo- 



