44 FOSSIL ASTEROIDEA. 



to the ultimate supero-marginal plate. As seen in the lateral wall of the disk the 

 heif^ht of the infero-marginal plates is slightly greater than that of the supero- 

 marginal series. The breadth of these plates adjacent to the median interradial 

 line on the actinal surface is 6 mm., or even a little more in an example whose 

 major radius measures 37 mm. and the minor radius 27 mm. The breadth of the 

 marginal border rapidly diminishes towards the extremity of the ray. The 

 surface of the infero-marginal plates is ornamented with extremely small and 

 closely crowded punctations, upon which traces of a minute, closely crowded, and 

 uniform granulation are preserved here and there. 



The adambulacral plates are small, about twice as broad as long, and their 

 surface is traversed by about three ridges, bearing punctures, running parallel to 

 the ambulacral furrow, upon which the spinelets composing the adambulacral 

 armature were articulated. There were about five or six spinelets in each lineal 

 series. 



The mouth-plates are regularly triangular, about twice and a half as long as 

 broad, and the two adjacent plates which constitute a pair form together a regular 

 rhomboid or lozenge-shaped figure. Their surface is covered with small, crowded, 

 rather coarse, irregularly disposed tubercles or granules (see PI. XV, fig. 2 d). 



The actinal intermediate plates are fairly large, and there is a distinct diminu- 

 tion in size towards the outer margin of the disk adjacent to the marginal plates. 

 The plates adjacent to the adambulacral plates are pentagonal, but a subhexagonal 

 or polygonal form elsewhere is the rule, with comparatively little irregularity. 

 The surface of the actinal intermediate plates is entirely covered with very small 

 equidistant punctations, upon which a uniform close granulation was previously 

 borne. Occasional small excavate pedicellarise are present here and there, the 

 lateral fossEe being slightly curved. 



Dimensions. — The type specimen is unfortunately fragmentary, and the radial 

 dimensions cannot be given. The length of one side of the disk, measured from 

 the tip of one ray to the tip of the adjacent ray, is about 41 mm. ; the breadth of 

 the supero-marginal plates adjacent to the median interradial line is 9 mm. ; and 

 the thickness of the margin is about 12 mm. 



In the fine example preserved in the Museum of Practical Geology, Jermyn 

 Street, figured on PL XV, fig. 2 a, the major radius measures 37 mm., and the 

 minor radius 27 mm. ; the length of one side of the disk measured about 

 42 mm., or probably rather more when complete ; the breadth of the infero- 

 marginal plates adjacent to the median interradial line is G mm. ; and the 

 thickness of the margin is 8'5 mm. 



Locality and Stratigraphical Position. — The type specimen is stated by Forbes 



