AMPHIURA. 
159 
ignorant of the anatomy of the upper surface of the disk and rays. I have not seen any 
other example of this rare form than the one I have figured, which belongs to the 
British Museum. Kg. 1 a shows the under surface of the natural size ; fig. 1 h, c, and d, 
are portions of the rays magnified four times to exhibit details of structure. Fig. 2 is a 
small specimen of the same species coiled up on a slab. 
Btratigrapliical position. — This curious Brittle-star was discovered by the late Mr. 
Pratt, F.G.S., in the Oxford Clay, and presents most of the characters of the genus 
Amphiura (' Linnean Transactions,' vol. xix, part ii, p. 150), to which it was referred by 
the late Professor Edward Forbes, F.R.S., in his notice of the species, in the ' Proceedings 
of the Geological Society,' vol. iv, p. 233. 
