74 HEMICIDAMS. 



the shell rises into a sub-conoidal form, with a prominent and elevated apical summit ; the 

 ambulacral areas are wide and nearly straight, so much so that I have received specimens 

 from France that were ticketed as Diadema ; the base of the areas is expanded, and there 

 are from six to seven pairs of semi-tubercles in this region, which are well spaced out and 

 very prominent, with a small granule at the angle of each zigzag interspace ; the upper 

 part of the areas has two marginal rows of imperforate granules, not very regular, however, 

 in their arrangement, and between them are several smaller granules, equally irregular in 

 size and disposition ; the poriferous zones are rather wavy and of moderate width ; the 

 pores have an elevated granule rising from the surface of the septa, and separating them, 

 which produces a moniliform line in the track of the zones ; the pairs of pores are nearly 

 horizontal, and unigeminal, from the disc to the equator; the zones at this point bend 

 outwards, to form enlarged spaces for the basal semi-tubercles ; as the zones approach 

 the peristome, the pores lie in triple oblique pairs. 



The inter-ambulacral areas at the equator are only twice the width of the ambulacral 

 areas (PL III, fig. 1 b), and, what is very unusual among the Echinidas, they are more 

 prominent than the ambulacra ; the primary tubercles are limited to the inferior and 

 middle parts of the areas, one or two only extending above the equator of the test (PI. Ill, 

 fig. 1 c) ; they are surrounded by areolas, which are confluent both above and below, and 

 have semicircles of five or six pustulose granules on their outer and inner margins. On 

 the upper part of the areas the true tubercles disappear (PI. Ill, fig. 1 a) ; the surface 

 of the tubercular plates in this region develops only clusters of granules, which are 

 very irregular in their mode of arrangement, but uniform in size and form ; the first 

 tubercular plates above those having true primary tubercles have a small imperforate 

 tubercle in the centre, and a cluster of granules around it, but the three or four plates 

 between this and the disc are covered with a homogeneous granulation ; the areolas of the 

 primary tubercles are separated from the poriferous zones by semicircles of granules (PI. Ill, 

 fig. 1 c), and like semicircles of scrobicular granules separate the areolas in the median 

 line from each other; there are from eight to ten plates in each tubercular column. 



The apical disc is large and very prominent, and forms a conspicuous elevation at the 

 summit of the sub-conoidal test (PI. Ill, fig. 1 a, e) ; the antero-lateral genital plates are 

 the largest ; the posterolaterals nearly equal them in size and figure, and the single plate 

 is the smallest ; the madreporiform body forms a kind of warty eminence on the surface of 

 the right antero-lateral plate, which is the largest ; the ocular plates are heart-shaped, and 

 project like tubercles from between the angles formed by the genital plates ; the surface of 

 all the elements of the disc, the genital, and even the ocular plates, is covered with 

 numerous granules. (PI. Ill, fig. 1 e.) 



The spines are only known by a fragment, which is imbedded in the base of a specimen 

 from St. Aubin de Langrune. This spine is thick and oval, with a ridge on one of its sides. 



The mouth opening is large, and the peristome is not deeply notched ; the anal opening 

 is obliquely oval. 



