172 Triassic Echinoderms of Bakony. 
of C. alata «gewohnlich an verkiirzten Individuen.... die Granulation auf dieser 
Seite ganz fehlt, dagegen eine Anzahl vom Scheitel ausgehender Furchen iiber 
dieselbe verlauft.... zuweilen nur bis in die Mitte des Stachels» — precisely as 
in C. semicostata. The grooves in C. semicostata may, according to Lause, extend 
to the collerette, and this further reduces the difference between the species. Chief 
stress is laid on the «processus laterales aliformes», which are said by LauseE to 
separate C. alata from all other Cassian species; but similar wing-like projections 
are shown in his figures of C. semicostata especially figs. 3 c, d, e, which may be 
compared with figs. 8 g & m of C. alata. The. margin of the acetabulum in 
C. alata is said to be smooth, but in C. semicostata either smooth or crenelate — 
only smooth according to Mtnster. Actual specimens do not support the attempted 
diagnoses any better than do the figures There remains the sole statement that 
in C. semicostata «die Gelenksgrube» is «vorgezogen und sehr ausgedehnt» («pro- 
tracta expansa»). I presume this to mean: directed towards the adapical surface of 
the radiole and widened transversely to that direction. This is not shown in the 
figures, and, in so far as any difference is visible in the specimens, which is. very 
slightly, it corroborates my view that the difference between the two forms is due 
solely to their position on the test. 
The relations of the normal C. alata to C. dorsata are of a different nature. 
It would be easy to prove, as many authors, from Minster downwards, have 
maintained, or suggested, or tacitly admitted, that no sharp line can be drawn 
between these two forms. It is easy to produce specimens that cannot be placed 
with certainty under one name rather than the other. Thus, the sole feature that 
distinguishes certain radioles of C. alata from certain of C. dorsata is the lateral 
keel; but this may be very slightly developed, and all stages may be observed 
between the somewhat flattened radiole more coarsely granular on the front than 
on the back, through radioles in which the granules along the sides are enlarged 
into spinules, and those in which the bases of these spinules have coalesced to 
form the lateral keels (see the three specimens in the British Museum, E 4514, 
handed over as C. dorsata by Kirstein, but transferred to C. alata by my prede- 
cessor, J. W. Grecory). The formation of a’keel is in fact merely an intensification 
of the natural tendency of the granules to lie in longitudinal rows. On the other 
hand, the available evidence contradicts the assumptions: that flattened, keeled radioles 
of «alata» type were associated in any individual with the more club-shaped 
radioles of «dorsata» type; that, for instance, one kind was confined to a particular 
region of the test while other regions bore the other kind; or that one kind was 
characteristic of the youth of an individual, the other kind prevalent in its age. 
That the contrary was the case appears to follow from the fact that radioles of 
«dorsata» and «alata» type respectively are found of all sizes as well as of various 
shapes that can be correlated with the different regions of the test. It is possible 
to sort almost the whole of the St. Cassian material-at my disposal into two series : 
alata and dorsata; and between these obvious series, intermediate forms are relatively 
few. Therefore, on the principles laid down in the paragraphs on Variation in the 
Radioles (p. 136), the distinction of the two species is justified. 
It is quite likely that these two ‘species, C. alata and C. dorsata, are both 
descended from a single ancestral species with more regularly claviform or baculiform 
peripheral radioles. “(wo bits of evidence point in this direction. | 
