540 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



Megistocrinus depressus (Hall). 

 Plate XLIX. Figs. 2, 3, and 4a-d. 



1862. Hall ; 15th Rep. N. Y. State Cab. Nat. Hist., p. lU. 

 1881. W. aud Sp. ; Revision Palaioer., Part II., p. 137. 



Syn. Mer/istocrinus Ontario Hall, 1862; 15tli Rep. N. Y. State Cab., p. 136. 



As large as the preceding species. Calyx depressed, wider than high ; 

 the dorsal cup basin-shaped ; the bottom part to the middle of the first cos- 

 tals — sometimes higher — flattened but not excavated ; the sides slightly 

 expanding to the top of the distichals, thence curving outward and forming 

 a short rim, from which the free arms are given off in pairs. Plates flat or a 

 little concave, thickened around their outer margins, and in well preserved 

 specimens covered by numerous very fine, somewhat irregular stria3, which 

 are more pronounced near the suture lines; the middle of the plates 

 sometimes slightly elevated, and the surface covered with small irregular 

 pustules. 



Basals small, only the points of the outer angles visible bej'ond the 

 column ; almost flat, and on a level with the radials ; the axial canal large 

 and indistinctly pentagonal. Distichals from one to three in the calj'x. 

 Three of the rays have a single distichal in both divisions, which is axillary 

 and followed by 2 X 2 short palmars, the other rays two additional distichals 

 and no palmars. Arm openings sixteen, arranged in eight pairs. The median 

 lines of the higher brachials are ornamented with indistinct, longitudinal 

 ridges, covered by similar striae as the other parts of the plates. Inter- 

 brachials : 1, 2, 3, with two or three irregular rows above, which meet the 

 interambulacral plates. First anal plate, which is a little larger than the 

 radials, iollowed by 3, 4, and 4 pieces, and these by a number of smaller 

 ones. Interdistichals one to three, arranged longitudinally ; the rays with four 

 arms generally having three, the others not more than two. Ventral disk 

 depressed-convex ; the food grooves marked by ridges, which diverge to the 

 arm bases ; the surface is covered by rather large, flat, irregular pieces 

 enclosing the orals and radial dome plates, which are but little larger than 

 the rest of the plates. Posterior oral in contact with the other.s, pentral and 

 spiniferous, while the other four are generally flat. Anus excentric. 



Ilorison and Locality. — Hamilton group ; Western New York and 

 Louisville, Ky. 



