NO. 8 EDRIOASTEROIDEA — BASSLER / 



lius, 1892, Pyrgocystis octogona'Richter, 1930, P. grayae Bather, 191 5. 

 P. atisticei Bather, 191 5, and P. batlieri Ruedemann, 1925, are the 

 other species of this genus. 



HEMICYSTITES Hall, 1852 

 (Hemicystis Haeckel, 1896) 



Theca a thin, flattened disk with oral arrangement and pitted plate 

 structure of Carneyella, but ambulacra are short, broad, and straight. 

 Anal pyramid elevated and composed of a circle of triangular plates 

 regularly arranged. 



Genotype.— H. parasitica Hall, 1852. Silurian (Rochester) of New 

 York. Agelacrinites hclliilus, hohemicus, confertus, latiusculus , sim- 

 plex, tenet', and velatus of Barrande, 1887, A. rectiradiatus Shideler, 

 1918, and Agelacrinus hilliiigsi Chapman, i860, Lehetodiscus youngi 

 Raymond, 1915, and L. chapmani Raymond, 1915, are described spe- 

 cies of Hemicystifes. 



THRESHERODISCUS Foerste, 1914 



Agelacrinitidae with branched ambulacral rays having a pronounced 

 trimerous origin. Interambulacrals large, squamose, imbricating in 

 central part and smaller along border. 



Genotype. — T. rainosits Foerste, 1914. Ordovician (Trenton) of 

 Ontario, Canada. 



AGELACRINITES Vanuxem, 1842 



(Agclacriiuts authors; Agelacystis Haeckel, 1895; Haplocystitcs Roemer, 1852; 

 Haplocystis Bather, 1899) 



Thin parasitic disks attached by entire aboral surface. Ambulacra 

 five, long, narrow, much curved; two (4, 5) to the right and three 

 (1-3) to the left. Interambulacral plates mosaic and sculptured, al- 

 though slightly imbricating. Periphery formed by several rows of 

 small plates followed by one row of much larger elongate ones. Anal 

 area a circle of triangular, regularly arranged plates. 



Genotype. — A. hamiltonensis \'anuxem, 1842. Devonian (Hamil- 

 ton) of New York. A. ephracuwrianus Bogolubov, 1926, A. hanoveri 

 Thomas, 1924, and A. rhenaniis Roemer, 1851, from the Devonian, 

 and A. hlairi Miller, 1894, A. legrandensis Miller and Gurley, 1894, 

 from the Mississippian are referred to this genus. 



