FROM THE UPPER CHALK. 229 



small single plate is imperforate ; the spongy portion of the madreporiform body is small, 

 and the surface of the other plates closely covered with granules. 



One remarkable feature in the structure of this test consists in the size, number, and 

 prominence of the miliary granules, which cover the inter-tubercular spaces and form on 

 the sides and upper surface of well-preserved specimens a thin incrustation which coats the 

 plates and makes the tubercles on the sides appear as punctured depressions rather than 

 elevations of the test. PI. LII, fig. 2 e, is a drawing of a portion of both areas with 

 the zones magnified four diameters, taken from the side of the test ; the inter-ambulacral 

 plates support three rows of tubercles, four or five in each, which are situated in a 

 depression surrounded by an areola, and have some of their bosses crenulated and 

 summits perforated (fig. 2 g, h). The ambulacra have four rows of similar tubercles and 

 a like abundance of close-set granules on the surface of their plates. The tubercles on 

 the basal plates are more numerous, the areolas wider, and the granules in a great 

 measure absent from this region of the test (fig. 2/) where these large basal plates are 

 situated, they are drawn, magnified four diameters. 



The mouth-opening is very small (fig. 2 b), about one third less than the vent ; the 

 peristome is nearly circular, thickened and prominent like the vent, the microscopic 

 plates of the inter-ambulacra being narrow and piled on each other produce the rounding 

 and thickening of the peristome ; the pores in the zones are unigeminal around the 

 opening. One remarkable specimen in my collection enables me to make these detailed 

 observations on the minute anatomy of the test of E. ahbreviatus. 



Affinities and Differences. — This species resembles E. subrotundm in the elevation of 

 the upper surface and inflation of the lateral parts. A comparison, however, of the 

 profiles of both species, as given in PL LH, fig. 1 c, and fig. 2 c, and PI. LHI, fig. 1 

 and fig. 2 c, will show at a glance several distinguishing characters, the excentricity 

 forwards of the apical disc, the shortness of the anterior slope, as compared with the 

 greater length of the posterior, and the prominence and recurvation of the single inter- 

 ambulacrum. In E. subrolundus the tubercles are larger and more numerous and the 

 miliary granides smaller and fewer, whilst the reverse forms one of the specific characters 

 of E. ahbreviatus ; the tubercles are small and sparse, and appear sunk in the test by 

 the great development of the miliary granulation which forms a thin coating on the 

 lateral and upper portions of the plates. In PI. LII both species are admirably drawn, 

 and the minute anatomy of the tests displayed, so that a careful examination of the 

 figures, will place the affinities and differences between these confluent forms more clearly 

 before the eye of the student, than the most elaborate description could convey to the 

 mind. 



Locality and Stratigraphical Position. — All the examples of this species that I have 

 examined were collected from the Upper Chalk at Harford Bridge, Trowse, and Trim- 

 mingham, Norfolk, where it is known as a leading fossil of the Norwich Chalk. 



