Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/83

Rh number towards the ambitus. The larger tubercles have a swollen scrobicule, a crenulated boss, and a small perforated mamelon, and the upper extremity of the boss has its crenulation projecting upwards and outwards like a frill (Pl. IV. figs. 3 & 4). The spaces between the tubercles are more or less crowded with larger miliaries; and these are again surrounded here and there by smaller. In the lateral interambulacra there are also several rows of the same kind of tubercles as in the anterior; the rows contain more tubercles, but do not approach the ambitus or the apical system more than do those of the anterior spaces. In the intcrambulacral spaces, between the large tubercles and the apical system are crowds of large and small miliaries.

The ambitus is sharply curved from above downwards, and is rendered irregular in its outline by the slight projection of portions of it from which the tuberculation of the actinal surface radiates inwards. On this surface (Pl. IV. fig. 2) the posterior ambulacra are bare and broad, and coalesce, forming a broad bare actinal shield, a few miliaries only existing. As a whole the actinal surface is flat, the mouth being very slightly sunken, and that only anteriorly; but between the ambulacra just noticed is a projecting plastron covered with secondary tubercles at the sides, and with miliaries on the top of its keel. The actinosome is large, elliptical, broader than long, and the sides are rounded and project slightly backwards. The posterior lip projects slightly, and has large miliary tubercles on it. The anterior phyllodes are well developed, and extend nearly to the edge of the test; and the posterior are recognizable by one or two large slit-shaped pores. The tubercles of the actinal surface radiate in lines from points in the lateral and anterior interambulacra at the ambitus, and the tubercles increase in size as they approach the actinosome with its comparatively bare surrounding plates. A very ill-developed, extremely narrow fasciole (visible under a magnifying power of 10 diam.) is seen on part of the test below the tubercular area. The frill-like crenulation is present on the actinal surface.

Length 2 inches, breadth 2 inches; height at posterior part inch, at apical system  inch.

Locality.—Mouth of the Sherbrook river, with Eupatagus Laubei.

The resemblance of this form to Maretia planulata, Gray, is perfect, with the exception of the partial and extremely small fasciole.

, sp. nov. Plate III. figs. 14–17.

The test is thin, and the outline of the ambitus is nearly circular, there being a slight flatness posteriorly where the anus is situate on a truncation which slants slightly from above downwards and inwards. The vertex is nearly central, and thence there is a slight slope to the apical system; the slope continues anteriorly, and then dips down suddenly to the ambitus. Behind the vertex a keel passes backwards horizontally beyond the line of the posterior ambulacral petals, and the slope increases to the margin of the periproct. The rest of the posterior part is obliquely truncate, the surface of the truncation being slightly concave from side to side.