FROM THE CORALLINE OOLITE. 401 



oblique, slit-like apertures, which are limited to the upper half of the rows (fig. 2 (^) ; in the 

 lower half, the pores are simple, like those of the inner row ; at the border, the holes are 

 so minute they cannot be distinguished ; at the base they are placed wide apart (fig. 1 b), 

 and near the mouth the ambulacra expand into phylloid expansions, which, near the 

 peristome, are contracted by large oral lobes. 



The inter-ambulacral areas are very unequal in width and development ; the anterior 

 pair are narrow, convex, and prominent ; they rise nearly perpendicular, forming with the 

 base an angle of 80°, and near the vertex curve backwards ; the plates on the inner sides 

 of the areas, as well as on the single ambulacrum, carry much larger tubercles than 

 the other dorsal plates (fig. 1 a, fig. 2 a) ; the posterior pair and the single area incline to 

 an angle of about 35°. The upper surface thus acquires the remarkable anterior elevation 

 which gives so marked a character to this species, and allies it with a Neocomian form — 

 Pygurus Montmollini, Ag. The single inter-ambulacrum possesses a central elevated 

 portion on its upper surface, made more apparent by two lateral depressions commencing 

 at the inner zone of the postero-lateral ambulacra, which gradually rise and blend with 

 the central elevation (fig. 1 c) ; this is continued downwards and backwards, and forms 

 the rostrated portion of the single area, which is slightly deflected at its termination 

 (fig. c, d). 



The apical disc is small and excentral, and nearer the anterior border ; it consists of 

 four small, perforated, ovarial plates (fig. 3), a single smaller, imperforate plate, and five 

 very small ocular plates, perforated near their centre ; the spongy, madreporiform body 

 rises from the surface of the right antero-lateral plate, extends into the centre of the disc 

 covering the inner portions of the ovarial plates, and having the ocular plates disposed 

 around its circumference. 



The under surface is concave, and very much undulated, the ambulacra forming narrow, 

 depressed valleys from the border to the mouth, and the basal inter-ambulacra extremely 

 convex eminences between them (fig. lb, c) ; near the mouth-opening their terminal 

 portions are developed into five tumid lobes. 



The large sub-central mouth-opening is directly beneath the apical disc; it is con- 

 sequently nearer the anterior than the posterior border ; the peristome is surrounded by 

 five oral lobes, which alternate with five phylloid ambulacra, filled with several longitudinal 

 rows of pores (fig. 1 b). 



The anal valley is a slight depression, formed out of a prominent portion of the basal 

 inter-ambulacrum; it has declining sides, covered with large tubercles, and is quite infra- 

 marginal ; the vent is oval, and elongated in the antero-posterior diameter (fig. 1 b, 

 fig. 1 c). 



The tubercles on the dorsal surface are very small, and arranged in five concentric rows 

 on each plate (fig. 2 b) ; they are encircled by sunken areolas, and the intermediate space 

 is covered with close-set miliary granules (fig 2 d). On the antero-lateral inter-ambulacra 

 and single ambulacrum the tubercles are considerably larger (fig. 1 a, fig. 2 a); at the 



