BATOCRINID^. 543 



the first costals and first interbrachials, then curving abruptly upward, widen- 

 ing a little in the upper part. Surface of plates, except basals and radials, 

 strongly nodose, the nodes cut up by irregular grooves or coarse wrinkles, 

 M'hich give to the species an extremely rugged appearance. 



Basals small, flat, disk-like, slightly depressed, only the points of the 

 angles projecting beyond the column ; central perforation large and pentalo- 

 bate. Radials, first costals, and first anal plate hexagonal and of nearly 

 the same size ; the second costals pentagonal, hexagonal, or heptagonal, 

 owing to the height of the interbrachials of the second row. Distichals 3X2 

 in the antero-lateral rays, decreasing in size ; the lower one almost as large 

 as the preceding axillary. The three other rays have but one distichal, and 

 2 or 3 X 4 fixed palmars, of which the upper one is short and curved like an 

 ai'm plate. Arm openings sixteen, arranged in groups of two and four; the 

 arm structure not known. Interbrachials : 1, 2, 3, 3, 3. Anal plate followed 

 by rows of 4, 5, and 4 plates, and a few irregular pieces at the arm regions. 

 Ventral disk depressed-subconical ; composed of numerous convex pieces; 

 the orals and radial dome plates large and spinous, and all isolated. Anal 

 tube excentric, strong at the base ; consisting of slightly elevated pieces with 

 spine-bearing larger ones interspersed. Column unknown. 



Horizon and Locality. — Hamilton group (Corniferous), Clark Co., Ind., and 

 Louisville, Ky. 



Megistocrinus concavus Wachsmuth. 

 Plate XL VIIL Figs. 5a, h, c. 



18S5. WicnsMUTH ; Proceed. Davenp. Acad. Nat. Sci., Vol. IV., p. 96, Plate 1, Pigs. 5, 6, 7. 

 1885. "W. aud Sp.; Revision Pateocr., Part III., p. 112. 



A rather aberrant form of the genus. Calyx wider than high, the ventral 

 disk higher than the dorsal cup ; the latter very shallow, abruptly depressed 

 to the top of the radials ; the first costals spreading horizontally, and form- 

 ing a wide and deep inverted cup ; the second bending abruptly upward so 

 as to place the upper part of the calyx almost at right angles to the trun- 

 cated lower part. Plates heav}^, and except the ba.^als, radials and first anal 

 plate, which are flat or a little concave, produced into broad, very prominent 

 knobs. 



Basals of medium size, forming a hexagonal di.sk, which occupies the 

 bottom of the concavity. Radials comparatively small, slightly bending 

 upwards, and constituting together with the lower margins of the first costals 



