230 THE FOSSIL ECHINOIDEA 



The apical system is excentric in front, its distance from the anterior margin being 

 rather more than one third of the length, or in the proportion of 0*38 : 1. The four 

 generative pores are rather closely placed, aad the anterior and the posterior pair are 

 equidistant. The odd anterior ocular plate is placed between the anterior generative 

 plates, and is small. The lateral ocular plates are much larger and subpentagonal ; 

 the anterior pair are placed in the angle formed by the junction of the anterior and 

 posterior generative plates, and the posterior pair are placed immediately behind the 

 posterior generative plates, and are separated by the considerable posterior extension 

 of the central madreporiform body. The ocular foramina are microscopic. 



The odd anterior ambulacrum is straight or slightly flexuous in its course ; and the 

 anteal sulcus is not apparent until near the margin, increasing gradually in depth and 

 breadth, and indenting the anterior extremity with a wide, but rather shallow, indenta- 

 tion, which terminates rather abruptly on the anterior interradia as seen from above. 

 The poriferous zones are nearly parallel, and are composed of pairs of very minute pores 

 obliquely placed, and rather wide apart from neighbouring pairs ; the interporiferous 

 area is flat, narrow, and of nearly uniform breadth throughout, excepting near the apex, 

 and is ornamented with numerous definite and rather isolated miliary granules. 



The anterior pair of petals are nominally flush with the surface of the test, 

 although the .depression of the poriferous zones in slight channels gives a rather promi- 

 nent appearance to the interporiferous areas; they are very long, and extend close to 

 the ambitus, widely divergent, subtending an angle of about 150°. Excepting at the 

 proximal and distal extremities of the petals, the poriferous zones run parallel to one 

 another. At the apical extremity the anterior zone of the petal converges gradually, 

 forming a graceful curve ; whilst the posterior zone is nearly straight in its course, its 

 convergence being scarcely perceptible. At the outer extremity of the petal it is the 

 posterior zone which converges, and forms the slight attenuation at the extremity, whilst 

 the companion anterior zone remains straight. In this manner there is a slightly sigmoid 

 character given to the petal, although its course, as a whole, might be said to be straight 

 from the apex towards the margin. The poriferous zones are rather broad and of 

 uniform breadth throughout, excepting at the extremities, where their attenuation 

 emphasizes very largely the curved character above noticed ; at the apical extremity 

 6 to 8 pairs of pores in each zone are so small as to appear almost aborted. The inner 

 pores are transversely oval, and the outer to a much greater degree, almost appearing 

 slit-like, and with a tendency to become pyriform ; the pairs are united by a conju- 

 gating groove, and adjacent pairs are separated by thin well-defined divisional costae 

 ornamented with a single line of miliary granules. The interporiferous area is a little 

 wider than the poriferous zone, and is ornamented with small definite and rather widely 

 spaced miliary granules of two sizes, indiscriminately mixed, the whole having a very 

 homogeneous appearance when seen with the naked eye. The posterior pair of petals 

 are longer than the anterior pair, and like them extend nearly to the ambitus ; their 

 course is straight from the apex towards the margin, and they subtend an angle of 

 about 47°. Their breadth is equal to that of the anterior pair, and their pharacter 

 and structure are similar, the terminal curvature, however, of the respective zones being 



