METOPASTER ZONATUS. 45 



to have been obtained from the Upper Chalk of Kent, but no indication of locality 

 is now preserved on the label. The example belonging to the Museum of 

 Practical Geology is from the Upper Chalk of Gravesend. 



History. — The type of this species, which was described by Forbes in his 

 memoir ' On the Asteriadge found fossil in British Strata ' (' Mem. Geol. Surv.,' 

 vol. ii, p. 473, 1848), originally formed part of Dr. Bowerbank's Collection, and 

 was first figured by Forbes in Dixon's ' Geology and Fossils of the Tertiary and 

 Cretaceous Formations of Sussex,' London, 1850, pi. xxii, fig. 4. That specimen 

 is now preserved in the British Museum, where it bears the register number 

 " E 2578." An accurate drawing of the type is given on PI. XVI, fig. 1 a, of the 

 present work. 



4. Metopasteb zonatps, Sladen. PL XII, figs. 2 a — 2 c. 



Body of small or medium size. General form depressed. Abactinal surface in 

 the fossil condition, as at present known, essentially concave in consequence of 

 the conspicuously upturned extremities of the rays. Actinal surface conformably 

 convex. Marginal contour pentagonal, with the radial angles slightly produced 

 and obtusely rounded, and the sides distinctly lunate. The major radius measures 

 nearly one-half more than the minor radius, or in the proportion of 3 : 2 approxi- 

 mately ; the actual dimensions in the example under notice being R := 27 mm., 

 r := 19 mm. approximately. Margin very thick in relation to the size of the disk, 

 and regularly rounded. 



The supero-marginal plates are four in number, counting from the median 

 inteiTadial line to the extremity, or eight from the tip of one ray to the tip of the 

 adjacent ray, exclusive of the odd terminal or " ocular " plate in each case. They 

 form a broad border to the abactinal surface of the disk, of uniform breadth 

 throughout, which measures about 8 mm. at the median intcrradial lino, in an 

 example whose minor radius measures 19 mm. Excepting the ultimate paired 

 plate all the supero-marginal plates are subequal, the breadth being nearly three 

 times the length, the actual measurements in the example under notice being 

 length 2'75 — 3 mm., and breadth about 8 mm. The abactinal surface of the plates 

 is distinctly convex along the median line of breadth, by which means each plate 

 is conspicuously defined. The general surface of the whole supero-marginal 

 series between the two ultimate plates is regularly rounded, and forms an uninter- 



7 



