pied Aric Piet! 
Descriptions of New Fossils. 179 
AGARICOCRINUS ELEGANS, Nov. Sp. 
Formula as usual in the genus. 
The type specimen is represented on Plate V. Fig. 4, azygous side ; 
4a, apical ; 4b, basal view. This beautiful species is represented by 
specimens in a very perfect state of preservation, of which the type is 
a fair example. The base is concave ; the dome is depressed convex. 
The plates of the radial series, and of the interradial series below the 
dome are regularly arranged. The large central apical dome plate is 
surrounded by six somewhat smaller plates, and two small ones on the 
azygous side. The opening on this side is surrounded by one row of 
regularly arranged pentagonal plates ; beyond these the arrangement 
is without regular order. The subdivision of some of the larger plates 
in the radial series of the dome affords an interesting caution as to the 
founding of species, in this genus, upon the number and arrangement 
of the plates in this portion of the fossil, as may be learned from fig. 4. 
The fragment of the column remaining, and which is shown in fig, 46, 
is round, and consists of equal, thin plates. Locality and formation 
same as the last. Extensive series of many species of this genus show 
that here the principle of differentiation into varieties seems to have 
reached its maximum. In many species the basal portion is deeply 
concave, forming a cup-shaped depression ; in others this depression 
widens and shallows, and in the A. crassus the base is even slightly 
convex. These variations of the pelvic portion are connected with 
equally remarkable ones in the amount of elevation of the dome, and 
the arrangement of the interradial series of dome plates. Equally 
remarkable are the species in regard to the varying thickness of the 
plates, some of the species, even when of small size, being composed of 
very heavy plates; while others are light and thin, reminding one of 
certain cystideans. I collected several hundred specimens of different 
species of Crinoids at the locality furnishing these types, and have 
since learned of the extension of this same bed of Echinoderma far to 
the south, where the specimens are equally abundant. 
——$____ 
THE AMERICAN ASSOCIATION FOR THE ADVANCE- 
MENT OF SCIENCE. 
The 30th meeting of the American Association for the Advancement 
of Science will be held at Cincinnati, commencing Wednesday, August 
ff, 1881. | 
The officers of the meeting are as follows: 
