28 FAUNA OF THE CORNBRASH. 



Order SELAGHIL 

 Family Cestbaciontid.e. 

 Genus ASTERACANTHUS, Agassiz. 

 Asteracanthus acutus, Agassiz. Plate I, fig. 6 a, h. 



1837. Asteracanthus acutus, Agassiz, Poiss. Foss., vol. iii, p. 33, pi. viii a, figs. 1, 2, 3. 

 1889. Asteracanthus acutus, A. S. Woodward, Cat. Foss. Fishes, B.M., vol. i, p. 313. 



Sldatijpe. — The following is the definition of Agassiz (modified, in square 

 brackets, by A. S. Woodward) : " More arched and decreasing more rapidly 

 towards the point than A. ornatissinins. The tubercles are arranged in two 

 strongly marked series and continue to the end of the ray. They are a little 

 elongated in the direction of the ray; those of the anterior border are largest. 

 Their base forms longitudinal ridges. One of these ridges at the anterior end 

 projects on the middle line of the ray [is keeled], hence the name. The posterior 

 surface is not so flat as in A. orTiatissimus ; its centre already rises above the 

 posterior furrow and rises still higher towards the end of the ray. On this surface 

 are seen two rows of [large] stained teeth [tubercles] pretty distant from each 

 other at their base, but approaching each other as they rise [arranged in close 

 series]. The inner cavity is considerable and extends nearly to the point of the 

 ray." " From the clay above the Cornbrash on the borders of the Ouse; at Castle 

 Mills, near Bedford." It has not been seen. 



Description. — One specimen only of an Asteracanth spine has been obtained 

 from the Cornbrash. The type of A. acutus not having been found, no direct 

 comparison can be made, but so far as the above description goes this specimen 

 agrees with it. It is broken at both ends, but extends for a length of 120 mm., 

 and has a breadth (partly by squeezing) of 25 mm. The anterior (convex) outline 

 has a radius of curvature of 270 mm. The ray is divided longitudinally into an 

 anterior ridged half and a posterior irregularly convex smooth half. The anterior 

 part is raised into 10 ribs, each of which has elongated tubercles, decreasing in size 

 distally and posteriorly. Each tubercle has a raised rim round its base, and 

 consists of a ridged cone, the ridges of which, when worn, show the underlying 

 material in the form of a white star, usually 5-sided. The anterior ones are in 

 definite rows, but the posterior are more irregular. The intervening substance is 

 furrowed longitudinally, the furrows being perforated with deep depressions. The 

 middle line has tubercles like the rest proximally, but for the great part, distally, 

 the intervening substance, with its furrows and perforations, rises into a triangular 



