Dr. T. Wright on the Cassidulidse of the Oolites. 315 



anus forms a blunter oval. A comparison of these specimens is 

 therefore very desirable, as size alone cceteris paribus does not 

 constitute a specific character. 



I have before me a large Pygurus from the Coralline Oolite of 

 Malton, Yorkshire, belonging to the collection of the Bristol 

 Institution, and kindly lent me for comparison by Mr. Etheridge 

 the curator. 



It so much resembles the Clypeaster Hausmanni, Dunk., in 

 proportional measurements, whilst it exceeds that Urchin in size, 

 that we think it identical with the German species : this Pygurus 

 measures in height 1 inch and T %ths ; antero-posterior diameter 

 5 inches and Toths; transverse diameter 5 inches and T 3 <jths. 

 The test is thin, the tubercles are small and numerous ; the am- 

 bulacra are prominent, projecting above the level of the interam- 

 bulacra, and describing similar petaloidal figures to those in 

 P. pentagonalis ; the ventral surface is inseparably united to the 

 rock, and a portion of the single interambulacrum is fractured. 

 Notwithstanding these defects, the likeness to C. Hausmanni is 

 so great, and the structural affinities so numerous, that we think 

 we are justified in our conclusion as to their identity : according 

 to Koch and Dunker the dimensions of Clypeaster Hausmanni are 

 — "Height 11 lines; antero-posterior diameter 4 inches and 

 7 lines ; transverse diameter 4 inches and 2 lines. L : B : H 

 = 100 : 90 : 20." The Pygurus before us exceeds therefore by 

 one-fifth in size this gigantic German Urchin. 



Locality and stratigraphical range. — Pygurus pentagonalis has 

 been collected from the upper rags of the Inferior Oolite at 

 Shurdington Hill : it is a rare Ifrchin in these beds, as I only 

 know of two in di vi duals having been obtained therefrom ; it has 

 been found in the Inferior Oolite of the district round Bath, and 

 was collected by Mr. Young and Mr. Phillips from the calcareous 

 grit of Yorkshire. P. Hausmanni, which in some respects re- 

 sembles our P. pentagonalis, was found in the Upper Coralline 

 Limestone of Kleinenbremen near Biickeburg. 



History. — I have not been able to compare our specimens with 

 those from the Coralline Oolite of Yorkshire, but have every 

 reason for believing that they are identical, although the figure 

 in Mr. Phillips's work is certainly more pentagonal than ours. 



In conclusion I take this opportunity of thanking Messrs. Bro- 

 die, Etheridge, Forbes, Fowler, Gavey, Jones, Lycett, Morris, 

 Strickland, Walton, Wayte, Waterhouse, and Woodward for the 

 loan of and permission to compare specimens, and Mr. W. II. 

 Baily for the care he has taken to make out the details of our 

 new species. I have subjoined a table which exhibits at one 

 view the range and stratigraphical distribution of the Urchins 

 described in the preceding papers. 



21* 



