﻿FROM THE CORALLINE OOLITE. 



397 



cave at the base ; the arabulacral petals on the dorsal surface are petalloid only in the 

 upper two thirds of their length, and very narrow and graceful in the lower third of the 

 areas (fig. 1 a, c ; fig. 2 a) ; the anterior border is emarginate and concave, and the under 

 side is impressed by the anteal sulcus ; the posterior inter-ambulacrum is rostrated and 

 deflected ; the mouth-opening is small, and the oral lobes large and prominent. When 

 these characters, which are permanent in all the examples I have examined, are compared 

 with the homologous parts in Pygurus Michelini, which have been already described, the 

 distinction between the species will be readily determined. (Compare PI. XXXV and 

 XXXVI.) 



Locality and Stratigrajj/iical position. — I have collected this urchin from the Lower 

 Calcareous Grit at Bullington-green, near Oxford, at Earringdon, Berks, from the same 

 rock at Scarborough, Castle Hill, and Gristhorpe Bay, on the Yorkshire coast. It is like- 

 wise obtained from the Coralline Oolite at Scarborough and Ayton, and at Malton and 

 Hildenley ; from the latter locality I have been enabled to study a fine large specimen, 

 kindly presented to me by C. W. Strickland, Esq., and beautifully developed by him. My 

 kind friend, John Leckenby, Esq., communicated the beautiful specimen figured in 

 PI. XXXVI, fig. 2 a, which came from the Coralline Oolite of Malton, and belongs to the 

 Scarborough Museum. The small specimen (fig. 1 a, b) was collected by my friend, Dr. 

 Murray, of Scarborough, from the Lower Calcareous Grit, near that town, and generously 

 given to me by him for this work ; Pygurus pentagonalis is, therefore, a true Corallian form, 

 and a most characteristic urchin of this formation, both in the Midland Counties as well 

 as in Yorkshire. 



Pygurus costatus, Wright, nov. sp. PI. XXXVII, fig. 1 a, b, c, d, e, /. 



Test sub-pentagonal, discoidal, much depressed at the upper surface ; ambulacral petals 

 large, costated, extending over four fifths of the upper surface ; anterior border flat, emar- 

 ginate ; posterior border rostrated ; postero-latcral border very thin ; apical disc excentral, 

 forwards; base flat; mouth-opening large, sub-central; peristome surrounded by five large 

 oral lobes and five spoon-shaped phylloidal floscnlcs. 



Dimensions. — One large specimen. — Height, one inch and one tenth ; transverse 

 diameter and antero-posterior diameters, equal, four inches. 



Specimen, PI. XXXVII. — Height, nineteen twentieths of an inch ; transverse diameter, 

 three inches and three tenths ; antero-posterior diameter, three inches and three tenths. 



Description. — This urchin is remarkable for its discoidal form and for the prominent, 

 costated character of its dorsal ambulacra ; the anterior border is flat, the sides form obtuse 

 angles near the middle of the disc, and the posterior border is rostrated, but not deflected ; 



