28 



neuce, in the upper part, which has an elongated azygous opening. 

 The plates covering the azygous area and bulbous prominence are 

 polygonal, variable in size, and fattened or concave. 



This species is distinguished from all others, heretofore describ- 

 (d, by the character of the regular interradials and azygous 

 plates, by the azygous area, and by having fourteen arms. After 

 having examined several hundred specimens belonging to this 

 genus, we believe that the number of arms do not vary within 

 the proper limits of a species, and hence the number of arms may 

 always be regarded as of specific importance. Other specific char- 

 acters will always be found in the interradial and azygous plates, 

 belonging to the calyx, but ditt'erences in the interradial plates 

 belonging to the vault will be found in the same species. There 

 is no increase in the number of plates belongiug to the calyx, 

 with increase of size, in the same species; but there may be an 

 increase, in the number of plates, in the vault, within the proper 

 limits of a species. 



This maguificient species was found by Prof. A. G. Wetherby, 

 in the Keokuk Group, in Tennessee, and is now in the collection 

 of Wm. F. E. Gnrley. 



AGARICOCRINUS TUODRIDM, U. sp. 



Fhiif ITT, Fig. 4, hasal view, Fi(j. 5, snmmit view: Fiij. 6", 

 azygous view of the same specimen. 



Species very large, subpentagonal in outline. Calyx broadly con- 

 cave centrally and rounding up to the arms and having a fanciful 

 resemblance to a hut, which suggested the specific name. The 

 plates of the calyx are concave or flattened, and are in striking 

 contrast with the tumid plates, in the species last described. 



Basals small and entirely hidden by the column. Fij'st primary 

 radials wider than long, a small part abruptly bent into the 

 columnar concavity, three hexagonal, two heptagonal. Second 

 primary radials one-fouth wider than long, quadrangular. Third 

 primary radials very large, even larger than the first, pentagonal, 

 axillary and in three of the rays, support on each upper sloping- 

 side three secondary radials, which gives to each of these three 

 rays two arms. In each ray adjoining the azygous area, there is 

 on one superior sloping side of the third primary ladial, three 

 secondary radials, and, on the other, a single secondary radial, 

 which is axillary, and supports on each upper side two tertiary 

 radials, which gives to each of these rays three arms. There are, 

 therefore, twelve arms in this species. The calyx is more protub- 

 erant, at the ends of the radials adjoining the azygous area, than 



