FROM THE CORAL RAG. 163 



but is distinguished from it by the greater size they attain in Hemipedina Marchamensis. 

 It resembles, likewise, Hemipedina Bouchardii, from the Kimmeridge Clay of Boulogne- 

 sur-Mer, but as that species has ten small tubercles on the inter-ambulacral areas, our 

 species, which has only eight, is distinct from it, whilst they both belong to that section of 

 the genus with numerous tubercles ranged on the same line on the plates. 



Locality and Stratiyraphical position. — This species was collected from the lower 

 Calcareous Grit of Marcham, Berks, and belongs to the collection of the Hon. R. Marsham, 

 who kindly communicated it for publication. 



Hemipedina Corallina, Wright, nov. sp. PI. XII, fig. 1 a, b, c, d. 



Test large, form unknown ; ambulacral areas narrow, with two marginal rows of 

 tubercles ; inter-ambulacral areas wide, equatorial plates with five or six tubercles on each ; 

 spines long and slender, stem nearly a uniform diameter and covered with fine, 

 close-set longitudinal lines, tubercles of both areas small and nearly of the same size. 



Description. — The diagnosis of this species is most imperfect, as I only know the 

 fragments of the test I have figured, which doubtless formed portions of large urchins ; 

 fig. 1 a was collected by Mr. Bean, from the Coralline Oolite of Malton ; the ambulacral 

 areas of this specimen have two marginal rows of small tubercles placed rather wide 

 apart. 



The inter-ambulacral areas are three times the width of the ambulacral. On the large 

 equatorial plates (fig. 1 b, c), there are four rows of primary tubercles abreast, with two 

 smaller secondary tubercles at the zonal side of the plates (fig. 1 c), which would give 

 eight rows of tubercles in the inter-ambulacral areas ; the areolas are wide and smooth, and 

 surrounded by circles of small granules (fig. 1 b, c). 



The mouth opening is large, and the jaws, which are preserved in situ, are powerful, 

 and armed with strong teeth (fig. 1 a). 



The spines are long and slender ; the head is short and stout (fig. 1 d) ; the stem 

 tapers very little ; the milled ring is prominent, and on it and on the surface of the stem 

 are numerous fine close-set longitudinal lines. 



Affinities and differences. — In the number of its tubercles in the inter-ambulacra, this 

 species resembles Hemipedina Marchamensis (PI. XI, fig. 1), but they are much smaller 

 in size, have much smaller bosses, and wider and smoother areolas than in that species ; 

 unfortunately, the fragments admit of no further comparison. 



Locality and Stratiyraphical position. — The fragment (fig. 1 a) was the only portion 



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