24 Dr. T. Wright on new Species of Echinodermata 
side of the areas, those of the right side alternating with those 
of the left ; interambulacral areas with two rows of primary 
tubercles, 9-10 in each row, so disposed that the test appears 
to possess only ten rows of primary tubercles nearly equidistant 
from each other ; spines long, numerous and hair-like. 
Height ,5,ths of an inch, transverse diameter z%ths of an inch. 
Description.—This singular little Urchin has been long known 
to collectors, and has been often a puzzle to them, for although 
a few specimens have been collected in a tolerable state of pre- 
servation, still for the most part the test is much injured by 
pyrites ; under the most favourable circumstances, it requires a 
good lens and much patient study to make out the details of its 
structure. It was first found in the black shales of the lower 
Lias near this town, and recently, with its hair-like spines at- 
tached to the test, from the same bed near Gloucester, when ex- 
cavating the new docks of that city ; it was there associated with 
Ammonites oxynotus, Quenst. It is difficult to say whether this 
tiny Urchin is a Hemicidaris or an Acrosalenia, and the absence 
of the apical disc leaves the question unsolved ; we incline to the 
opinion that it is an Acrosalenia from the structure of the am- 
bulacral areas, the shape, length and development of the spines 
when compared with the diameter of the test, the spines being 
more than four times the diameter of the latter ; be this however 
as it may, it is neither an Echinus nor a Cidaris, as previous 
authors have supposed. The ambulacral areas are narrow, with 
two rows of small marginal tubercles not much larger than the 
common granulation of the test; these tubercles are placed im 
each row at some distance apart, and the tubercles of the one 
side alternate with those of the opposite side ; between these rows 
of tubercles the surface of the plates is adorned with a delicate 
granulation, which is arranged into a zigzag line; the tubercles 
are very uniform in size and distribution throughout the areas, 
and do not increase at the base thereof, as is the case in the ge- 
nus Hemicidaris. The interambulacral areas are wide, and have 
two rows of primary tubercles, from 9-10 in each row; their 
mammillary eminences have well-defined areolas, the summits of 
the mamme are deeply crenulated, and the tubercles are small 
and widely perforated ; the areolas are confluent above and be- 
low ; between the two rows of tubercles an elevated band extends 
from the mouth to the apical disc, composed of from 4—6 rows 
of unequal-sized granules. When viewed at the equator with 
the naked eye, this Urchin appears to possess only ten rows of 
tubercles placed nearly equidistant from each other ; but when 
examined with an inch object-glass under the microscope its 
true structure is disclosed,—the narrowness of the ambulacral 
