Echinoid Tests, Cidaroida. 93 
and 4 mm. from the concave (adoral) margin, occupies with its scrobicule the 
greater part of the plate, and projects about 2.1 mm. The perforate mamelon is 
depressed hemispheroidal, with a diameter of 2.1 mm.,; its neck long, slightly undercut, 
resting on a crenelate platform of 3.2 mm. diameter, with about 18 crenellae. The 
scrobicule appears slightly sunk and marlted with radiating folds, but the appear- 
ances are not very clear, owing to weathering and matrix. There is no trace of 
a scrobicular ring; but outside the scrobicule are irregular miliaries. 
The adradial margin shows no trace of denticles, only an elevation parallel 
to the margin on the inside. It is much worn. 
Relations of the Specimen. — In some respects this plate resembles 
M. planus; but its proportions are different: the scrobicule appears relatively wider, 
and it is hard to suppose that, had there been a scrobicular ring, all traces of it 
should so entirely have disappeared. The specimen is, without doubt, a Miocidaris, 
but is not well enough preserved to support a specific name. 
Miocidaris >, sp. indet. 6. 
(Plate VII. figs. 161—163.) 
Material. — Part of an ambulacrum from the Cassian beds of Cserhat 
(Leitnerhof). 
Description of the Specimen. — The fragment contains about 
8 ambulacrals on each side. These are distinct, and lie approximately at right angles 
to the perradius. 
The perradial tract bears small, mamelonate, imperforate, non-crenelate main 
tubercles, one on each ambulacral, therefore forming two alternate rows; and in 
the space between the rows are miliaries, apparently without regular arrangement. 
In at least one case these miliaries take the place of a main tubercle. Within this 
tract the ambulacrals are slightly bent towards the apical pole. 
From the perradial tract, the ambulacrum slopes gently to the outer edge 
of the poriferous tract, whence it slopes more steeply to the margin. The pores 
are slightly oval transversely, and set obliquely, the inner one being, as is usual, 
nearer the adoral border of the ambulacral plate than is the outer one. They are 
neither conjugate, nor separated by any noticeable elevation. The sutures between 
the ambulacrals are clear, and slightly sunk, but there is no definite groove along 
them leading from the inner pore. Neither is there any groove or depression between 
the outer pore and the edge of the ambulacrum, although perhaps the faintest 
tendency towards such a groove may occasionally be detected. Consequently the 
outer edges of the ambulacrals have not a double scollop. 
On the inner surface (fig. 161) the perradial tract is smooth and shows no 
sutures. The two pores of each pair lie in a groove, but are not actually connected 
by the groove, since they are separated by a slight ridge crossing it obliquely. 
Width of theambulacrum . . . . . +... ». ». 40 mm. 
» Sree re DEMACIAL TAC Bee ue wv Lo A > 
Diameter of a main tubercle . ....... O04 » 
Height of an ambulacral : 3. 3; « . .. . » O4D > 
Relations of the Specimen. — This ambulacrum differs from those of 
Triadocidaris persimilis and T. subsimilis in the absence of grooves leading from the 
