bo 
o 
or 
Morphological Results. 
hand, are still far from having attained the characteristic structure. Of Mesodiadema 
unfortunately we have no certain ambulacrum, but, as stated in the diagnosis of 
the genus, the ambulacrals are still distinct and in simple series; in the genotype 
M. Marconissae the ambulacra are relatively narrow, and the only feature that 
suggests a Diademoid relationship is the incipient peripodium in which each pore- 
pair lies. «Ces ambulacres» says pe Lorton (1882) «se rapprochent beaucoup de 
ceux des Cidaris.» The phrase in the generic diagnosis, «ambulacrals never tuber- 
culate» («Ambulacralzonen nur granulirt» Neumayr) must not be understood to mean 
more than that the ambulacra bear no tubercles approaching primary tubercles in size. 
De Loriox’s statement, no less than his figure 1b, copied by Neumayr, shows that 
each ambulacral bears an admedian tubercle and miliary quite as distinct as those 
in Triadocidaris persimilis. Atracut (1905, p. 2) says of his Mesodiadema Lam- 
berti: «Ambulacri stretti, diritti, colla zona interporifera coperta di granuli, tra i quali 
uno o due sulla faccia superiore si sviluppano in modo tale da raggiungere quasi 
le dimensioni dei tubercoli interambulacrali>. Of course in the adapical region (sulla 
faccia superiore) the primary tubercles of the interambulacrals (tubercoli interambula- 
crali) are not very large, so that if each perradial tract (zona interporifera) only 
bears one or two approaching them in size, it would seem that this species really 
has the ambulacral tubercles less developed than has M. Marconissae. The obscur- 
ity of Dr. Atracui’s figures and the ambiguity of his comparison with M. Mar- 
conissae prevent me from using them to check the correctness of my interpretation. 
The two Diadematoid ambulacra from the Cassian beds of Sections XI and 
VI (pp. 125—127, Pl. IX, figs. 214—217) are particularly interesting in this connec- 
tion. The primary ambulacrals and their pore-pairs are still in simple series, and, 
so far as the sutures are visible, the plates appear equal in size; the ambulacra 
also retain the streptosomatous union with the interambulacra characteristic of most 
Triassic Cidarids. On certain plates, however, the tubercles have grown larger and 
extend across the suture on to the adjacent ambulacrals. There is no trace of an 
arrangement of the plates in triads, or of the pore-pairs in arcs of three, since the 
distribution of the larger tubercles is rather irregular, and, where most regular, they 
correspond with two rather than with three plates. The ambulacrum 7 from the 
Raiblian beds of Jeruzsalemhegy has the larger tubercles more pronounced, but still 
irregular; it further approaches the Diademoids in the conjugation of its pores. 
In both $ and 7 the pore-pairs are nearer the oblique position found in the Diadem- 
oida than they are in the other ambulacra from Bakony. It should of course be 
remembered that this obliquity of the pore-pairs is found in some Cidarids, especi- 
ally in the adoral region, while it is not manifest in several true Diademoids. 
The further evolution of the Diademoid ambulacrum through the Liassic species 
need not here be followed. There also the several features may be seen in various 
stages of development, and to some of them allusion has already been made in the 
preceding pages. The two points of importance arising-from the present study are, 
first, that the Diademoid modification had already begun in Cassian times; second, 
that these earlier forms show an obvious resemblance to the ambulacra of Triad- 
ocidaris and Miocidaris. 
The relations of the interambulacrals in many Diademoida have already been 
discussed at great length (see especially pp. 102—117). It has been shown that 
the streptosomatous union of the interambulacra with the ambulacra passed up into 
