282 PYGASTER. 



P. Morrisii has a greater number of tubercles in the ambulacral and inter-ambulacral 

 areas, P. laganoides having four rows in the ambulacral and fourteen in the inter- 

 ambulacral areas, whilst P. Morrisii in the same region of the corresponding area possesses 

 six rows and twenty : two rows. 



P. Morrisii resembles P. Gresslyi, Desor, in its general form, in the size and dis- 

 position of its tubercles, and in their surrounding granulation, but P. Morrisii is more 

 depressed, has a larger anal opening, and more rows of tubercles in both areas. 



Locality and Stratigraphical position. — This rare species was collected by Mr. W. Buy 

 from the Forest Marble or Cornbrash near Stanton, Wilts. The specimen figured 

 (PI. XX, fig. 1) is the only one I know. I have seen a Pygaster from the Great Oolite 

 near Cirencester, which resembles my urchin ; but the specimen was crushed, and not 

 otherwise determinable ; it had the same number of tubercles in the areas as P. Morrisii. 

 I dedicate this species to my friend Professor John Morris, to whose valuable labours 

 British palaeontologists are under so many lasting obligations. 



C. Species from the Coral Pag = 14 e Mage Corallien, d'Orbigny. 



Pygaster umbrella, Agassiz. PI. XX, fig. 2 a, b, c, d, e,f. 



Pygaster umbrella. Agassiz and Desor, Catalogue raisonne, Ann. des. Scienc. Nat., 



3" serie, torn, vii, p. 144, 1847. 



— — Bronn, Index palseontologicus, Bandi, p. 1066, 1848. 



— — D'Orbigny, Prodrome de Paleontologie, torn, i, 13 e etage, 



No. 510. 



— Edwardseus. Buvignier, Statistique geologique, pal^ontologique depart, de la 



Meuse Atlas, p. 46, pi. 32, figs. 31—33, 1852. 



— umbrella. Wright, Memoirs of the Geological Survey, Decade V, pi. 8. 



Note on British Pygasters, 1856. 



— — Cotteau, Etudes sur les Echinides Foss., p. 194, pis. 27, 28, fig. 1, 



1856. 



— — Desor, Synopsis des Echinides Fossiles, p. 165, 1857. 



Test large, more or less elevated, sometimes circular, oftener sub-pentagonal ; ambu- 

 lacral areas narrow, with two complete marginal rows of tubercles, and two incom- 

 plete rows, which commence near the peristome, and extend only half way up the 

 sides ; inter-ambulacral areas wide, with from sixteen to eighteen rows of tubercles at the 

 equator, which are small and rather irregularly disposed on the upper surface, but 

 large and arranged in regular horizontal and vertical series at the circumference and 

 base ; anal opening distinctly pyriform, occupying rather more than one half the length 



