Dr. F. A. Bather—A Cidarid from Hartwell. 303 
The measurements in millimetres are as follows :— 
Upper plate. Lower plate. 
Height . 65 6°05 
Apicad- interradial margin . 
Orad-interradial margin 
Height of scrobicular circle 
Width 
Diameter of boss (ill- defined, say) 
Width of serobicule ,, a 
Diameter of platform ; 
Vertical diameter of mamelon 
Transverse Hi 
From this it will be seen that the perebieular circle is compressed, 
so as to be somewhat elliptical transversely ; the scrobicules, however, 
remain distinct. Taking the general thickness of the extra-scrobicular 
region as 1-4 mm., including the tops of the secondary tubercles, the 
boss rises, with a slightly convex curve, to a platform at 1 mm. above 
this. The platform is marked with twelve distinct crenelle. The 
mamelon, which expands slightly, reaches *8 mm. above this. 
The interradial tract is covered with secondary tubercles, of which 
five lie in a lineal space of 4.4mm. They tend to run in lines 
approximately parallel to the two limbs of the interradial margin. 
The boss of a secondary tubercle may have a diameter of as much as 
‘7mm. Between the secondary tubercles are scattered much smaller 
tertiary tubercles, which occasionally form partial scrobicular rings. 
The main tubercle can hardly be said to have a ring of scrobicular 
tubercles, for the tubereles surrounding the scrobicule are certainly 
not larger or more regular than the other secondary tubercles. Indeed, 
they seem in some cases to be smaller, as though invaded by the 
_ main scrobicule. On the intertubercular tract bordering the apicad 
margin of the upper plate there can be distinguished a line of these 
tubercles, gradually diminishing in size. On the corresponding tract 
of the lower plate there is an irregular ridge, but the tubercles from 
which it has been derived have atrophied. 
The species which this specimen most resembles are two found 
near Boulogne-sur-mer, namely Ctdaris legayi Sauvage & Rigaux 
(1872) and Cidaris boloniensis [melius bononiensis| Wright (1857), 
neither of which has yet been recorded from England. Descriptions, 
-Grawings, and bibliography of these will be found in G. Cotteau, 
Paléontologie Frangaise, Jurassique, vol. x, part 1, EchinidesRéguliers, 
pp. 214 (1877) to 226 (1878), pls. 200-202. In C. bononiensis, as 
compared with the present specimen, the scrobicules are more 
distinct, the scrobicular ring more complete, and the scrobicular 
tubercles more developed in comparison with the other secondary 
tubercles. In C. legayi, Cotteau’s figure shows the scrobicular 
tubercles as less pronounced than in C. dononiensis, but still as more 
pronounced than the secondaries; his text, however, states that they 
are of almost the same size as the latter. Our specimen therefore 
seems to lie between these two species, but rather on the side of 
C. legayt. 
C. bononiensis comes from the Kimmeridgian, C. degayi from the 
Portlandian zone of Ostrea expansa, that is to say, the Upper 
Portlandian. he Hartwell Clay is generally regarded as Lower 
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