FROM THE INFERIOR OOLITE. 335 



types of Lamarck's species. In fact, Echinobrissus dunicularis^ Llhwyd, may be regarded 

 as the type of that section of nucleolites in which the anal valley extends from the border 

 to the apical disc, and Echinobrissus scutatus, Larak., of that smaller section in which 

 the anal valley never extends from the border to the disc. 



Professor M'Coy* described three nucleolites under the names planulatus, pyramidalis, 

 and aqualis. The two latter forms appear to be varieties of E. dunicularis, and planulatus 

 a variety of E. scutatus. I have not seen the original specimens which belong to the 

 Cambridge Museum ; but the author having kindly furnished me with outlines of these 

 urchins to assist me in identifying his species, I have formed that opinion from his 

 figures. 



This urchin exhibits much diversity as regards size, outline, height, and tumidity. Its 

 most typical forms are found in the Inferior Oolite and Cornbrash, and one of the best 

 specimens I know is that from the cabinet of my friend, the Rev. A. W. Griesbach, which 

 forms the subject of our figure. The suite of specimens before me from these terrains vary 

 from a sub-orbicular to a sub-quadrate outline, and present nearly all the intermediate forms. 

 They are rounded anteriorly, a little contracted before, enlarged at the sides, and more or 

 less bilobed posteriorly. The upper surface is convex, and exhibits various degrees of 

 elevation ; in some it is much depressed, in others it rises into a sub-conical form. In a 

 series of specimens before me scarcely two have the same proportional height. The vertex 

 is almost always excentral and inclined towards the anterior border ; but the amount of 

 inclination, like the height, varies considerably in different individuals. 



The ambulacral areas have a petaloid or lanceolate figure, with sub-parallel sides ; the 

 single area and the anterior pair are nearly of the same length and width, and the 

 posterior pair are the longest and widest (fig. 1 a, c). The poriferous zones vary in 

 structure on the dorsal and ventral surfaces ; in the petaloid portion of the dorsal surface 

 the pores of the inner row are round, those in the outer row are oblong, and the furrow 

 uniting the pores varies in depth in different examples (fig. 1 /) ; in a large specimen 

 there are about forty pairs of pores in the petaloid portion of the dorsal zone ; between 

 each pair there is a short row of small microscopic granules which separates the outer 

 oblong pores from each other (fig. 1/). In all the non-petaloid portion of the zones, the 

 pores are small, round, and very indistinct (fig. \ e) ; at the sides and outer third of the 

 base, near the mouth, however, they become more distinct. 



The inter-ambulacral areas are of unequal width ; the posterior pair are nearly one 

 fourth wider than the anterior pair, and the single area is the widest (fig. 1 a). The anal valley 

 extends from the posterior part of the disc to the border ; it is narrow above, wider in the 

 middle, and expanded below, in the excavated portion ; it has vertical parallel walls, which 

 gradually diverge, then approximate, and afterwards expand outwards, forming a well- 

 defined groove (fig. 1 a). The pyriform anal opening is situated at the extreme end of the 



* 'Annals of Natural History,' 2(1 series, vol. ii, p. 416. 



44 



