118 Triassic Echinoderms of Bakony. 
The peristomial margin has a faint convex curve, with a slight but distinct 
interradial excavation. The matrix on the inner surface prevents one from seeing 
whether the margin has any thickened ridge. There are seen, however, two strong 
interambulacral processes, apparently rising rather steeply from the floor of the 
interambulacrum, then bent sharply over adapically ; their precise outlines are obscured 
by matrix, which has not yielded to several days’ work. (Figs. 196, 197). 
Description of Specimen b. — This is a fragment similar to a, but smaller, 
and obviously from a younger individual of the same species. The a column contains 
4 fully developed tubercles, and the remains of another on the peristomial border. 
The inner half of the next interambulacral at the adapical end is also preserved. 
The 5 column contains 5 fully developed tubercles. The fragment differs from the 
holotype in the following respects: — The sutures between the interambulacrals are 
clearer. The interradial depression is a trifle clearer, and comes up to the peristome. 
The mamelons are distinctly excentric, towards the adapical side of the tubercles. 
The interradial excavation of the peristome is a trifle more marked. The denticles 
are not distinct. The perignathic girdle is represented by a ridge continuous across 
the interradius; no processes are bent over aborally. (Figs. 192—194). 
The following are measurements of the two specimens in millimetres: 
Specimen @ Specimen b 
Length of adambulacral margin of a column (4 plates) . . . .. . 44 3.2 
» > » > 3b" 9 i(Suplates)) eo) 5.1 not preserved 
Measurements of two plates in the b column 1st. Sth. 1st. Sth. 
Heights or vertical diameters)". S @2 7 ye ee cape O mea) 0.65 0.85 
Transverse diameters. {2 //2)4-)) <6) eye ee Ay ee ne 2.6 ca.4.6 
Distance of centre of tubercle from margin of plate . . . . . 19 2.2 11. cals 
Diameters of, tabercles )-:. 2 pau, oh), ee eae ok Lo 0.5 0.7 
» x “mamelons,) 2 420 n,n ey ee too obscure 
Thickness in the middle of the interambulacrum at the 5th. plate, 0.5. Towards 
the margin is a considerable thickening and then a sudden thinning; these and 
other measurements are obscured by matrix. Distance of that point from adoral 
margin, ca. 5.2. Thickness at highest point of interradial processes in a, 3.1. 
Relations of the species. — In the lowness of its interambulacrals and 
the consequent confluence of the scrobicules to such an extent as to render them 
almost square rather than circular, M. margaritatum appears to differ from all the 
known species of Mesodiadema. Other distinctive features that it is possible to mention 
are: in M. Marconissae the imperfect scrobicular ring, the larger relative size of 
the tubercles and their greater distance from the adambulacral margin; in M. Lam- 
berti, the confusion of the tubercles with miliaries on the oral surface; in M. simplex, 
the smaller size, the less numerous and less developed tubercles, which are «au 
bord adambulacraire». 
Mesodiadema lata n. sp. 
(Plate VIII, figs. 198—211). 
Diagnosis. — A Mesodiadema with main interambulacral tubercles well devel- 
oped, probably throughout, and having scrobicules confluent, slightly elliptical, 
definite; the area broad and slightly sunk. The width of an interambulacral being 
taken as 100, its height averages 25 (the extremes are 19 and 40), distance from 
centre of tubercle to adradial margin averages 47.8 (extremes 34 and 58), transverse 
