120 GLYPHOCYPHUS 



Genus — Glyphocyphus, Haime, 1853. 



Arbacia (pars), Agassis, ISSfi. 

 EcHiKOPSis (pars), Agassiz, 1&46. 

 Hemidiadema, Agassis, 1846. 

 Temnopleuea (pars), Sorignet, 18.50. 

 GLYniociYPHCs, Jules Haime, 18.53. 



— Besor, 18.56. 



— Cotteau, 1839. 



The Urchins forming this group have a small circular test, more or less inflated above 

 and concave below. The poriferous zones are straight, depressed, and composed of uni- 

 geminal pores throughout. The primary tubercles of both areas are nearly of the same 

 size. The boss, with its crenulated summit, is surrounded by a distinct areola, and sur- 

 mounted by a small niammillon minutely perforated at the vertex. The ambulacral and 

 inter-ambulacral plates are marked with sutural depressions, which are wider and deeper 

 on the plates of the latter areas ; the surface is covered with fine, close-set homogeneous 

 granules, nearly uniform in size over the whole test (PI. XXIX b, figs. 1 and 2). The 

 apical disc is a small annular structure, solidly united to the test, and forming a narrow, 

 sHghtly elongated, oblong ring, composed of five ovarial and five ocular plates, articulated 

 alternately together on the same line around the vent aperture or periprocte (fig. 2 b). 

 The ovarial plates are the largest ; they have a triangular shape, with tubercles external 

 to the annulus, and a large hole at the apex ; the right antero-lateral plate is the largest, 

 and supports the niadreporiform body. The rhomboidal ocular plates are wedged in 

 alternately on the same line with the ovarials ; and the portion external to the annulus is 

 covered with numerous granules. Mouth-opening is small, subcircular, and sunk in a 

 slight depression ; peristome decagonal, divided into lobes by feeble incisions. 



The genus G///p/ioc//jj/ais forms among the Diademad^ with crenulated and perforated 

 tubercles a very small group, in which the ambulacral and intcr-arabulacral plates are 

 marked with angular impressions, and their surface covered with prominent close-set 

 granulations. The solidity of the apical disc, and its firm articulation to the coronal 

 plates, with the regularity as regards size and arrangement of the tubercles in both 

 areas, form an assemblage of characters which readily distinguish the small Urchins of this 

 group from their congeners. A considerable difference of opinion has prevailed amongst 

 Echinologists regarding the true characters of the forms now comprised in this genus, 

 arising, doubtless, from the smallness of the individuals themselves, the imperfect pre- 

 servation of most of the specimens, and the destruction of many of the essential structures 

 that distinguish them, M. Cotteau, however, had lately at his disposal a fine series of 



