from the Lias and Oolites. 35 
depth of the poriferous avenues being greater than the suleus 
which divides the interambulacra. 
The mouth is large and decagonal, and lies in a concave 
depression in the base, surrounded by the larger tubercles 
which occupy this region of the test. The ovarial plates are 
small, and form a rather prominent ring around the anal open- 
ing; the eye-plates are small, but in some of the foreign indivi- 
duals now before me the eye-holes are very distinct. 
Affinities and differences.—This Urchin resembles Arbacia 
Forbesii, but may be distinguished from that species by having 
the ambulacral areas proportionately wider, the tubercles larger 
and opposite to each other, and the poriferous avenues having 
the pedal holes in triple oblique pairs; it belongs moreover to a 
newer rock of the Oolitic series. 
Locality and stratigraphical range-—We know only one English 
specimen of this species, which was found in the Cornbrash by 
Mr. Buy near Sutton Benger, Wilts; on the continent it occurs 
in the Baireuthian Jurakalke, where it was found by Count Min- 
ster. It has been collected from the Great Oolite of Langrune 
by Prof. Deslongchamps and M. Tesson, and from the Calcaire a 
polypiers at Ranville by M. Michelin. We beg to record to each 
of these gentlemen our best thanks for the beautiful series of 
type specimens of this Urchin with which they have so liberally 
supplied us. 
History.—Figured and described for the first time by Gold- 
fuss. We are not aware that any detailed description of the spe- 
cies has been given before, with the exception of the very brief one 
contained in the ‘ Petrefacta Germaniz.’ 
Polycyphus Deslongchampsii, Wright. PI. I. fig. 4, a-e. 
Test hemispherical, circumference circular ; ambulacral areas 
with two rows of larger and two rows of smaller tubercles ; 
interambulacral areas with two rows of larger and several rows 
of smaller tubercles ; the small tubercles in both areas often 
degenerating into mere granulations ; basal tubercles large 
and prominent. 
Height ,/,ths of an inch, transverse diameter 15ths of an inch. 
Description —Amongst the many beautiful forms of Urchin 
structure, this pretty little species will bear comparison for neat- 
ness and symmetry with any of the family to which it belongs. 
We found the first specimen about eighteen months ago, and since 
then have added an interesting series to our collection. It must 
be a rare form, as only two or three specimens have been obtained 
besides those collected by ourselves. - The ambulacral areas are 
one half the width of the interambulacral, and have one row of 
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