128 Triassic Echinoderms of Bakony. 
Width’of/‘ambulacrum/ 57. ".4;.-% -alaecirca46) mm 
Width, of perradial jiractic-)j0% $9) acinea e127) mam: 
Diameter of a large main tubercle . . . . . 0.9 mm. 
Height of an ambulacral AP ae res OYE hentia 
The inner surface of the ambulacrum shows no sutures. There is a median 
flat perradial tract. The poriferous tracts are marked with shallow transverse 
grooves, which run from the perradial tract to the margin, and correspond with 
the pore-pairs. (Fig. 219). 
Relations of the Specimen. — In the nature of the tuberculation, and in 
the conjugation of the pores, this ambulacrum seems more advanced than « & &, 
although the true Diadematid type, with the ambulacrals in triads, is not yet attained. 
General remarks on these Ambulacra. — Intermediate as they are 
between the Cidarid and the Diadematid types, these fossils prove the contempor- 
aneous existence of some primitive Diadematids. In the possession of tubercles 
they disagree with the diagnosis of Mesodiadema, while the distribution of the 
tubercles is different from that of Hemipedina and Diademopsis. The difference in 
this respect between different regions of the same ambulacrum is a clear~sign of 
changing character, the unituberculate primaries showing the road along which the 
species has travelled, while the growth of certain tubercles and the consequent 
partial fusion of the ambulacrals into majors point to the direction in which it is 
going. Here it may be remembered that «Cidaris» olifex Qurnst. has an ambulacrum 
of similar character (see p. 114), and it is particularly noteworthy that in that 
species the larger tubercle may be on every second ambulacral as in our specimens. 
Thus, although it is impossible to connect these ambulacra individually with any 
of the interambulacrals from Bakony, they lend support to the view that some of those 
interambulacrals are those of early Diadematids in a similar transitional stage of 
development. Once again we are forced to the conclusion that the change from 
Cidaridae to Diadematidae was one that took place slowly by almost imperceptible 
steps, which can be traced in the life-history of a single individual. 
Remains of the Jaw-apparatus. 
The Triassic rocks of Bakony have yielded 14 fragments of the lantern, distri- 
buted as follows among the various horizons: 
portions of 
pyramids rotulae teeth 
Muschelkallk 53) '.) se 2 — — 
Cserhat pronpe.. 2) ene 2 — 
Jeruzsalemhegy group. 9 — 1 
The peculiarities of this distribution probably depend on the small size of the 
objects, which renders their collection a matter rather of accident than of design. 
All these fragments are of the type of structure presented by the recent Cidaridae, 
but such observations as have hitherto been published do not make it clear that 
this type is confined to that Family; it might have persisted in the early represen- 
tatives of the Regularia Ectobranchiata. Therefore speculation concerning the parti- 
