CIDARITID A. 315 
beyond the spines, so as to reach objects the latter could 
not touch. 
2. Echini, which differ from the above in the tubercles 
being imperforate, and the ambulacral area wide : the spines 
and tubes are of a moderate size. 
3. Diademe.— The tubercles are perforated, and the 
ambulacra wide and studded with large tubercles. 
4, Salenie.—The tubercles are imperforate, and _ rela- 
tively large ; the chief distinction is a solid ovarian disk on 
the summit, composed of several large flat plates, anchy- 
losed together. 
The case of the Turban Echinites is composed of twenty 
vertical series of plates, the ambulacra, or porous grooves, 
forming continuous bands from the summit to the mouth, 
which is armed with five angular teeth. This tribe comprises 
many of the most elegant fossil species ; those which, from 
their shape and highly ornamented surface, have received 
the popular name of Fairy’s night-caps. The genus Cidaris, 
which is characterized by perforated spinous tubercles, 
affords the most beautiful examples, and these are occa- 
sionally found with the spines in contact ; a circumstance 
less rare than might be supposed, when the nature of the 
attachment of these organs is considered ; for, upon the 
decomposition of the integument, and the ligaments which 
connect the spines with the tubercles in a living state, 
these appendages quickly fall off, even in recent specimens. 
The interesting fossil figured LZign. 100 (ante, p. 311), is 
a choice example of a Cidarite with the spines attached. 
This species (Hemicidaris crenularis, Agassiz) is said to be 
characteristic of the Upper Jura limestone of Switzerland, 
and was supposed to be identical with Mr. Parkinson’s 
Cidaris papillata var. (Pict. Atlas, pl. lvi. fig. 6), from Calne, 
in Wiltshire ; but spines like those of Lign. 100, do not 
occur in the English oolite. These spines are not homo- 
geneous throughout ; the central part appears to have been 
