l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



ambulacral plates. The genotype, A. hamiltonensis Vanuxem (pi. i. 

 fig. 18), originally figured in a reversed position, is a handsome fossil 

 of the Hamilton group of New York. A. rhenanus Roemer, 185 1, 

 from the Devonian of Germany, selected as genotype of Haplocystites 

 by Roemer and later changed to Haplocystis by Bather (pi. i, figs. 12, 

 13), proves to be founded upon a mould of the underside of part of 

 the oral disk of a typical Agclacrinites. A. blairi Miller, 1894, from 

 the Warsaw limestone at Boonville, Missouri, was incorrectly figured 

 since the type specimen shows that the rays curve as in typical 

 Agclacrinites (pi. 7, fig. 9). A. Icgrandensis Miller and Gurley, 1894, 

 was based upon a mutilated specimen showing only four ambulacra, 

 but our illustration (pi. 4, fig. 13) of an excellent example in the 

 Springer collection from the same horizon and locality, shows a nor- 

 mal number and arrangement of the ambulacra. 



AGELACRINITES SOUTHWORTHI, n. sp. 

 Plate 4, fig. 12 



This handsome species is based upon a specimen perfect in all 

 details except that the left posterior ray and the adjoining interambu- 

 lacral plates are slightly crushed and in part destroyed. As our photo- 

 graph shows, the structure of the rays is similar to that in the geno- 

 type, but their length falls far short since they end a little distance 

 beyond their angle of curvature. The interambulacral- plates, which 

 are large, smooth, and imbricating, differ markedly from the sculp- 

 tured polygonal, very slightly overlapping plates of the genotype. A 

 closer relative is perhaps A. hanovcri Thomas (pi. 7, fig. 10) from 

 the Shell Rock division of the Devonian at Mason City, Iowa, in 

 which the ambulacra are very similar, but a ridge composed of the 

 inner rows of encircling plates is present, and the arms are still 

 shorter. 



The specific name is in honor of Charles Southworth, of Thedford, 

 Ontario, whose researches in the Hamilton rocks of Ontario have 

 brought to light many fine fossils. 



Occurrence. — Hamilton (Arkona beds, 20 to 30 feet below the 

 Encrinal limestone), Marsh's Mill, Arkona, Ontario. 



Holotype.—V.S.^M. no. S-3478. 



ISOROPHUS Foerste, 1916 



In this genus the oral area is covered by numerous small plates and 

 an extra series of ambulacral covering plates often occurs between 

 the usual two rows. The interambulacral plates, scalelike and more or 



