82 BULLETIN" 88, UNITED STATES NATIONAL MUSEUM. 



" Adambulacral plates more prominent [less prominent than the 

 inframarginal plates], slightly wider than long, and numbering, on 

 each side, from 9 to 10 [probably not less than 16 in each column]. 

 Ambulacral pieces a little wider than long, not alternating with the 

 adambulacral plates, and each provided with a rather sharp ridge 

 across most of its width. 



"There are 10 oral plates [oral armature] formed by the junction 

 of the adambulacral rows, which in form and size are scarcely dis- 

 tinguishable from the other plates of those series. 



" Greatest breadth measuring between the opposite extremities of 

 the rays ; 0.7 inch; breadth of rays at their inner ends, 0.1 inch; 

 length of same, 0.3 inch; diameter of madreporiform piece, 0.02 

 inch." 



Formation and locality. This small species appears to be common 

 at a very restricted horizon near the base of the Eden formation 

 (Fulton beds), exposed at low water mark in the Ohio Biver in the 

 eastern portion of Cincinnati, Ohio. 



Remarks. Not one of the twenty examples seen is well preserved 

 and all the plates are more or less separated. The general structure 

 seems to be that of Mesopalseaster. The composition of the axillary 

 area is not positively ascertainable but one specimen shows what 

 appears to be a large axillary interbrachial plate (see pi. 7, fig. 5), 

 distally surmounted by two somewhat smaller inframarginals. This 

 is probably the true structure since it is so in all the smaller Meso- 

 palseasters, as M. lanceolatus, M. parviusculus, M. granti, and M. 

 proavitus. 



The differences between M. finei and M. proavitus are not great. 

 The former is a smaller species with less plates in all of the ranges, 

 more prominent axillary inframarginal and axillary interbrachial 

 plates, and is also found at a lower geological horizon. M. finei 

 differs from the small species M. parviusculus of the earliest Siluric 

 in having more plates in all of the columns. M. granti is a larger 

 species and with smaller and more numerous plates than in M. finei. 

 M. lanceolatus is probably the most closely related to M. Jinei but is 

 distinguished abactinally by the diagonal arrangement of the plates 

 on each side of the radial columns. 



Cat. No. 60604, U.S.N.M. 



MESOPALJEASTER(P) LANCEOLATUS, new species. 



Plate 4, fig. 3. 



Measurements: R = 4.5 mm., r=1.3 mm., R = 3r ) . 



Rays short, stout, distinctly lanceolate actinally and rapidly ta- 

 pering abactuially. Disk comparatively large, abactinally convex. 

 Interbrachial arcs distinct but small. 



Abactuially the disk has a ring of large, strongly stellate plates 

 which are the basal plates of the radial and supramarginal columns. 



