INVERTEBRATES. 209 



from that species than A. inomatus of Hall is. So that if we unite A. aster iscus 

 and A. eequibrachiatus, we would apparently have to include A. inomatus also. 

 To one unacquainted with the imperceptible gradations by which such an ex- 

 tremely divergent form as this is connected with the Batocrinus group, it would 

 seem like an unnatural arrangement to include it; yet it is so connected as not 

 to be separable more than specifically from others that shade into the typical 

 forms of Batocrinus. 



Locality and position: Upper part of Burlington limestone, Lower Carbonif- 

 erous series, Burlington, Iowa. 



Genus AMPHORACRINUS, Austin. 



Synon. — Ilelocrinites (sp.), Goldf. Nov. Act., vol. xix, p. 341; (not in Petref., vol. i, 

 p. 197, 1826). 



Amphora (sp.), Cumberland, 1826. Reliquiffi Oonservatse, p. 36. 



Actinocrinus (sp.), Portlock, 1843. Report Geol. Lond., p. 347, and of vari- 

 ous others; (not Miller, 1821). 



Melocrinus (sp.), Bronn, 1848. Index, p. 719. 



Amphoracrinus, Austin, 1848. Quart. Jour. Geol. Soc, Lond., vol. iv, p. 292; 

 (not Roemer, 1852. Bronn's Leth. Geog., Yol. ii, p. 250, tab. iv, fig. 15). 



Dorycrinus, Roemer, 1853. Wiegm. Arch., p. 207. 



The generic formula of this group is precisely that of Actinocrinus, with per- 

 haps the exception of more generally having a small number of anal and inter- 

 radial pieces. It is distinguished from that genus, however, by having the 

 opening of the summit lateral, directed outwards, and penetrating a thickened 

 protuberance composed of small pieces. In some instances the opening is not 

 much more lateral than in particular examples of section (c) of the true Actino- 

 crinus group, which consists of species without a proboscis; but even in these 

 cases it still differs in being directed outwards, or in being placed upon, or 

 rather penetrating, a protuberance, which usually extends down the anal side, 

 so as to separate the two posterior rays more widely than the others ; while the 

 arm-bases are nearly always more in groups, and more protuberant than in 

 that section of Actinocrinus. Again, the species of Amphoracrinus are usually 

 distinguished from the typical forms of A.ctinocrinus in generally having the 

 second primary radial pieces quadrangular, instead of hexagonal, and the body 

 plates, with very rare exceptions, without radiating costse. In the latter 

 characters they agree with the Batocrinus group, from which, however, they 

 are readily distinguished by their lateral opening without a proboscis, as well as 

 by nearly always having their arm-bases and the adjacent parts forming five 

 protuberant lobes. They likewise differ from all sections of Actinocrinus, as 



27 Sept. 4,1866. 



