INYERTEBEATES. 211 



importance, is nevertheless a constant one: that is, the second primary radial 

 pieces in Megistocrinus are always hexagonal instead of quadrangular, as is most 

 generally the case in Agaricocrinus and Amphoracrinus. Again, Megistocrinus 

 always differs from Agaricocrinus in having the body much more prominent 

 below the arm-bases, and the vault proportionally more depressed. 



The three species that have been supposed to show a complete transition 

 from Megistocrinus, through such forms as Actinocrinus unicornis, into the Am- 

 phoracrinus group, i. e., Actinocrinus hrevicornis, A. minor and A. superlatus, Hall 

 (the types of the last two of which are now before us), seem to us to be true 

 Megistocrinus. They have exactly the form and physiognomy of that genus, 

 with which they agree in all points of structure not probably due to age, and 

 in having all their second radial pieces hexagonal instead of quadrangular; 

 while the typical specimens of the species A. minor and A. superlatus show that 

 the opening is placed on the side slightly lower than the arm-bases, and instead 

 of being surrounded by a thickened protuberance, presents abruptly projecting, 

 fractured, thin edges, like the base of a small lateral proboscis, precisely as we 

 see in the typical species of Megistocrinus. It is also worthy of note that Prof. 

 Hall describes the other species (A. hrevicornis'), as having a " proboscidiform 

 aperture." Hence we regard these three forms as true Megistocrinus, and pro- 

 bably young individuals. 



We are not sure the genus Amphoracrinus commenced its existence as far 

 back as during the Upper Silurian epoch, though some Hamilton group (Devo- 

 nian) species described in New York seem to belong to it. It was during the 

 deposition of the Subcarboniferous rocks, however, that it attained its maximum 

 development, and became extinct. 



The law of priority would, perhaps, compel us to adopt Cumberland's name, 

 Amphora, for this genus, were it not for the fact, that the species he evidently 

 regarded as the typical one was a true Actinocrinus. Cumberland gave no 

 generic description, but figured and described two species under the name 

 Aphora. He used no specific names, but numbered the species "1st species" 

 and " 2d species." His first species, in the text, is the second on the plates. 

 Of the first species, he says (p. 37) "the plates of this fine specimen, which 

 is entirely hollow, are remarkably emarginated with broad borders, resembling, 

 on its outer form, an earthen wine Amphora, with five handles for suspension 

 and a central neck to pour from." Hence it is evident the name was suggested 

 by this first species; and as it is a true Actinocrinus, Amphora becomes merely 

 a synonym of that genus, as it is, in part, of Amphoracrinus of Austin, to which 

 group his second and only other species belongs. 



