03 MESbZOIC RADIATA. 



siderably shorter and more steeply inclined than the posterior ; 

 mouth small, deeply impressed; primary tubercles large, scat- 

 tered. 



This species in size and form of the base resembles the P. um- 

 brella (Lamk. sp.) [Clypeus semisulcatus, Phil.), but is more ele- 

 vated ; and while in the profile of that species the posterior side is 

 much the shortest and most highly inclined, the proportions of 

 the present fossil are precisely reversed, a character which also 

 separates it from the other known species. The tuberculation is 

 as large, but more scattered than that of the P . patelliformis (Ag.). 



Not uncommon in the inferior oolite of Dundry* 



{Col, University of Cambridge.) 



Dysaster symmetricus (M^Coy). 



Sp. Char. Regularly oval (length 10 lines, width 8^ lines, depth 

 6^ lines), anterior and posterior ends equal in size and con- 

 vexity, neither of them sinuate ; uniformly gibbous, except a 

 small subangular prominence at the apex of the anterior am- 

 bulacrum, and the middle of the base which is slightly con- 

 cave, the margin of the base being obtusely rounded except in 

 front of the mouth where it is concave — it is most tumid at the 

 opposite end ; mouth small, rather more than one-third of the 

 length from the anterior end ; anus high on the posterior face, 

 the shell beneath is not sinuate, evenly convex ; ambulacra of 

 moderate and nearly equal width, the posterior pair meet just 

 over the anus, the anterior one does not quite reach to the 

 other two, the point of convergence of which is two-fifths the 

 length of the shell distant from that of the posterior pair. 



The symmetry of the two ends separates this species at a 

 glance from its congeners. 



Not uncommon in the inferior oolite of Bridport. 

 [Col. University of Cambridge.) 



Dysaster subringens (M'Coy). 



Sp. Char. Nearly orbicular, faintly subpentagonal by the pro- 

 jection of the interambulacra, depressed, but the height rather 

 more than half the length (length 1 inch 1 line, width the same, 

 height 7 lines) ; dorsal surface evenly convex ; oral surface 

 radiatingly undulated by the shallow concavity of the am- 

 bulacral spaces, and the gentle gibbosity of the interambu- 

 lacra, the posterior one most prominent ; each interambulacral 

 plate seems on the oral face nodulous in its middle, forming 

 two obsolete rows of nodules on each ridge ; mouth nearly 

 central ; anus a little above the posterior margin ; three an- 

 terior ambulacra meeting at the centre of dorsal surface, very 



