84 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



There are therefore at the base of the rays no less than 11 columns 

 of plates. The radial columns proximally have a tendency to become 

 less distinct and indistinguishable from the accessory pieces. The 

 plates in general are highly convex, granular and abundantly spine- 

 bearing. There are not less than 20 plates in each supramarginal 

 series. 



Madreporite highly convex, broadly oval in outline and radially 

 striated. 



Inframarginal plates finely granular, highly convex, subquad- 

 rangular in outline and increasing in size slowly proximally. About 

 23 in each column. 



Adambulacral plates like the inframarginals but not increasing 

 much in size proximally, with about 29 in each column. As in other 

 species of this genus, each plate bears three prominent spines, two 

 laterally and one ambulacrally. 



Ambulacral plates one to each adambulacral plate, and with a 

 sharp ridge which medially bends abruptly orally. Podial openings 

 as in other forms of Mesopalseaster. 



Interbrachial areas occupied by single axillary interbrachial plates 

 upon each of which rest proximally two axillary inframarginals. 



The specimens are not figured, as an illustration can not readily 

 be made. 



Formation and locality. Three more or less entire specimens and 

 fragments of four rays were found by Dr. E. O. Ulrich in the Eden 

 shale exposed back of Covington, Kentucky, at an horizon about 

 100 feet above low water in the Ohio River. All the specimens a^e 

 now in the Herzer collection, a part of the late Prof. James HalFs 

 private collection, recently purchased by the University of Chicago. 



Remarks. M. proavitus and M. granti are closely related, since 

 both have 11 columns of abactinal plates, including the marginals, 

 and they are nearly alike actinally. However, the former is twice as 

 large and appears to have more conspicuous radial and supramarginal 

 columns than the latter. These differences and the further fact that 

 one occurs in the Utica and the other in the earliest Siluric will serve 

 to distinguish the two species for the present. M. proavitus may 

 prove to bo identical with M. (?) wilberanus, which see for further 

 remarks. 



MESOPAL^ASTER (?) WILBERANUS (Meek and Worthen). 



Petraster wilberianus MEEK and WORTHEN, Proc. Acad. Nat. Sci., Philadelphia, 



for 1861, vol. 13, 1862, p. 142. 

 Palseaster wilberanus HALL, Twentieth Rep. N. Y. State Cab. Nat. Hist., 1868, 



p. 285; rev. ed., 1868=1870, p. 328. 



Original description. "This beautiful starfish resembles rather 

 closely Petraster rigidus of Billings, 1 but is smaller, and has more 



1 Decade 3, Org. Rem. Canada, pi. 9, fig. 3o. 



