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 jj^jths of an inch, transverse diameter ^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 y 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 in 

 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 mammae 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 



