﻿60 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 47 



convex, or occasionally having the form of a low cone. Arms sixteen, 

 four in the anterior and postero-lateral rays, two in the antero- 

 lateral rays. Arrangement of calyx plates similar to that of other 

 sixteen-armed species (see fig. i). Arm bases rather small, forming 

 a continuous row around the calyx, without interradial depressions. 



Tegmen moderately elevated, not depressed between the arm bases, 

 composed of numerous small, convex plates. The radial dome plates 

 and a variable number of other tegmen plates bear short spines. Anal 

 tube situated about one-third the distance from the center to the 

 dorsal margin. 



Column circular, with large, obscurely pentalobate canal. 



Remarks. — This species is closely related to Megistocrinns spin- 

 osulus Lyon, but differs in having sixteen arms instead of forty, 

 and the anal tube is less eccentric. The plates of the dorsal cup, 

 though strongly convex, are less distinctly spinose. A single in- 

 dividual has seventeen arms, i. c, three in the right antero-lateral 

 ray, but as it is otherwise similar to eight specimens having sixteen 

 arms, this may be regarded as an abnormal feature. The largest 

 specimen studied measures 27 mm. in height, and 36 mm. in greatest 

 diameter; the smallest is 15.5 mm. high, and 22 mm. in diameter. 



Formation and locality. — Middle Traverse or Alpena limestone : 

 Richard Collins' quarry, 1 Alpena, Michigan. 



Cat. No. 36,013 (holotype), Rominger collection, and 35,144 

 U. S. N. M. 



MEGISTOCRINUS SPHiERALIS n. sp. 



(Plate XV, 1, ia~b.) 



Description.- — Body nearly spherical in form, but slightly flattened 

 at the base. 



Surface of the basals elevated above the radials, forming a hexag- 

 onal plate which is nearly covered by the proximal plate of the 

 column. Each plate of the dorsal cup, with the exception of the 

 radials, bears a short spine. The radials may be ornamented by low 

 ridges, or they may be smooth. Spines of the higher calyx plates 

 cone-shaped, becoming more slender and longer as they approach 

 the region of the arms. 



Arms sixteen, arranged in a continuous row around the calyx, 

 without interradial depressions. There are, as usual with this num- 

 ber of arms, four each in the anterior and postero-lateral rays, and 

 two in the antero-lateral rays. The arm openings arc large .and 

 vertical in position. 



1 Grabau, Ann. Rep't Geol. Surv. of Mich, for igoi, p. 176. 



