546 THE CEINOIDEA CAMEEATA OF NORTH AMERICA. 



(?) Megistocrinus abnormis (Lton). 

 Plate XLIX, Figs, la, i, c. 



1857. Actinocrimis abnormis — Lyon ; Geo). Rep. Ky., Vol. IH., p. 479, Plate 4, Figs. 1, la, b. 

 1865. Megistocrinus abnormis — -Shumaed; Catal. Palajoz. Foss. N. Amer., p. 3S0. 

 1881. Megistocrinus abnormis — W. and Sp, ; Revisioa Palseocr., Part U., p. 137. 



This species is remarkable for the large lobes at the arm regions, which 

 give to tlie calyx a distinctly pentalobate outline, with deep interradial 

 notches. Dorsal cup saucer-shaped, a little flattened at the bottom ; the 

 plates thin, flat or slightly concave, and devoid of ornamentation. 



Basals in the same plane with the radials, forming a flat hexagonal disk, 

 of which only a narrow margin is visible be^'ond the column ; central canal 

 large and obtusely pentangular. Radials and costals nearly of equal size. 

 Distichals 3 X 2 in the two antero-lateral rays, supporting the arms ; the 

 three other rays have an axillary in each division and 2X4 palmars. Prim- 

 ary arms sixteen ; arranged : Iji. Interbrachials : 1, 2, 3, 3, 3 ; the first as 

 large as the radials; those of the second row about the same size as the 

 distichals; the plates of the third row considerably smaller; the middle 

 pieces of the fourth row often located in the tegmen. Interdistichals one or 

 two; there are generally two in rays with four arms, and the lower one 

 rests upon the truncated middle part of the preceding axillary, but where 

 there is but one it occupies the notch between the first distichals. Anal 

 interradius extremely wide and somewhat flattened ; the first anal, which is 

 fully as large as the radials, often supports four plates in the first row, and 

 five to seven in the second and third. Tegmen highly convex, composed of 

 medium sized, irregular, flat pieces, the ambulacra marked by ridges, and 

 the interambulacral spaces by depressions. Orals in contact ; the posterior 

 one and the radial dome plates strongly tuberculous or subspinous, forming 

 six conspicuous prominences upon the surface. Anus located a little above 

 the arm bases, opening out through the fiat surface of the tegmen. 



Horuon and Localibj. — Corniferous ; Louisville, Kj^, Clarke Co., Ind., 

 and Marian Co., Ky. Very abundant in some localities, but good specimens 

 quite rare. 



Tyfes in the Lj-on collection. 



RemarJcs. — This is not a typical Megistocrinus, and we have referred it 

 with much hesitation to that genus. It departs from the typical form in the 

 wide and deep depressions at the arm regions, in the flattening of the anal 



