Diadematoid Radioles. R. lineola. 233 
from the Lias, figured by QuenstepT (1875, pl. Ixvii, ff. 11—19) as Cidaris amal- 
theoides and allies, but those have more numerous thorns. 
The micro-structure has been studied in a radiole from the Quarry near 
Cutting I (Pl. XVIII, fig. 458). In this are seen only an axial lumen, with a diameter 
about one quarter that of the shaft, and a wall of radiate septa. The section is 
elliptical and the septa are much clearer near the long axis of the ellipse; here they 
are straight, thick, and almost wedge-shaped, but apparently perforate. They are 
united by trabeculae, which are rather stout in the adcentral region of the wall. 
At the sides of the ellipse, the septa follow a curved course, and, as they are 
followed to the other end of the ellipse, seem to merge into the trabeculae; or one 
may describe thc septa as arranged in two systems, those of one system cutting 
across the other, as in watch-turned engraving. A similar arrangement sometimes 
occurs in other forms of echinoderm stereom, and we have already noticed something 
of the sort in the trulliform radioles of Anaulocidaris. At the sides of the ellipse 
the boundary of the lumen is distinct, but it is not so at the ends. 
In this section the coarser septa, where they crop out on the surface are 
about 16 to the millimetre; but in other radioles they seem to be about 20 to the 
millimetre (fig. 429), 25 (fig. 425), or even finer. It is, however, very difficult to 
calculate exact measurements on these rounded surfaces, and thin sections of this 
material are rarely clear enough to be of use. 
Relations of the Species. — The general form, the striation, and the 
hollow lumen appear to characterize a long series of radioles from the beginning 
of the Muschelkalk, or earlier, to the end of the Lias. The plates of the test or 
other remains associated in several instances with such radioles prove that they 
cannot all be referred to a single species. The descriptions of the radioles hitherto 
published do not permit intelligible and distinct specific diagnoses to be based on 
those skeletal elements alone; an extension of Hessr’s work is required; meanwhile 
we recognize as fresh characters of diagnostic value the relations of the axial canal 
or axial complex, and the size of the longitudinal striae. By these features C. lineola 
may be distinguished from superficially similar forms of Keuperian age. It is, 
however, very difficult to distinguish these radioles from those of Cidaris grandaeva 
Apertt (1834 ex Gotpr. MS.) a species said to range almost right through the 
Muschelkalk. The general form and superficial characters of normal radioles of 
C. grandaeva as described and figured by ALBertr (1834, p. 96) Scumip & ScHLEIDEN 
(1846, pl. iv, f. 8), Quenstept (1852, p. 574, pl. xlviii, f. 33), ScHaurotu (1855, 
p. 529, pl. iii, f. 6), Desor (1858, p. 160), ALBertr (1864, p. 54), and QueENSsTEDT 
(1875, p. 158, pl. Ixvii, ff. 102, 109, 115, ff. caet. excl.) agree with those of the 
normal C. lineola. Examination of four radiole-fragments of C. grandaeva borne 
on a small slab of Trochiten-Kalk from Crailsheim (Brit. Mus. E 8536) shows further 
resemblance as regards the two characters mentioned above. On three of the 
fragments the striae are from 30 to 32 to 1 mm., and in a transverse section of 
1°2 mm. diameter there appears to be an axial canal of 0°4 mm. or one-third the 
shaft diameter. These numbers agree with some specimens of C. lineola. Hessr, 
however, after examining several radioles of C. grandaeva says (1900, p. 215) 
that their micro-structure is of the normal Cidaris type, a statement implying that 
the shaft possesses both an axial complex and a cortex (axialer R6hrencomplex und 
Deckschicht), The former of these at least would afford a point of distinction, 
