Dr. T. Wright on the Cassidulidse of the Oolites. 309 



apices remote ; pores widely apart ; interambulacral arese nearly 

 of the same width ; vertex central ; apical disc excentrical, and 

 inclined backwards ; anal opening of an oblong form, situated 

 in a shallow valley in the middle of the single interambulacrum ; 

 between the upper anal border and the disc there is a consi- 

 derable undepressed portion of the test ; base flat and very 

 slightly undulated ; mouth nearly central, pentagonal, and sur- 

 rounded by five prominent lobes ; the tubercles on the dorsal 

 surface are quite microscopic, those on the base are a little 

 larger and more distinct. 



Height 2 inches and j%ths, antero-posterior diameter 4 inches 

 and /(jths, transverse diameter 4 inches. 



Description. — This noble Urchin preserves the conoidal eleva- 

 tion of its dorsal surface in all the individuals we have examined. 

 The circumference is nearly orbicular, the antero-posterior being 

 somewhat greater than the transverse diameter ; the dorsal sur- 

 face of the test is uneven in consequence of the ambulacra form- 

 ing concave depressions, which have a petaloidal form, and are of 

 a nearly uniform width ; the single area and the inferior pair are 

 the longest, the latter are much inclined, and the posterior pair 

 are slightly flexuous ; the central space between the pores is nar- 

 row, and lies lower than the general surface of the interambu- 

 lacra. The pores are situated at a considerable distance apart on 

 the dorsal surface and become approximated at the basal angle, 

 where they fall into close-set pairs, from thence to the mouth 

 they are arranged in triple oblique rows ; the pores are extremely 

 small and indistinct on the basal surface. The interambulacral 

 arese are very uniform in width and convexity on the dorsal sur- 

 face, the anterior pair are the longest, and the single area has a 

 remarkable form arising from the shallowness of its anal valley, 

 and the superficial position of the anal opening which forms an 

 oblong depression in the middle of the area ; between the upper 

 border of the opening and the disc there is a smooth, slightly de- 

 pressed portion of the test to the extent of an inch, which is the 

 rudiment of the furrow so much developed in some Nucleolites, 

 and which forms one of the most important diagnostic characters 

 of our species ; from the lower border of the opening the test is 

 depressed, the limits of the depression being bounded by two ele- 

 vations; the basal angle of this area is very slightly produced and 

 deflected, the posterior lobes are entirely obsolete. The vertex is 

 central, and at a short distance behind it the apical disc is situated, 

 which is considerably inclined towards the posterior border, and 

 formed of an anterior and a posterior pair of perforated ovarial 

 plates, and a single imperforate plate with a large central portion, 

 having a spongy madreporiform body attached to its surface, and 



