278 PYGASTER. 



horizontal and vertical rows, the ambulacral areas are not so lanceolate, the anal 

 opening is wider in the upper part, and does not descend so far down the inter-atnbulacrum 

 as in P. umbrella, in which it has a well-marked pyriform shape, and is much contracted 

 in the upper part like a key -hole. (Compare PI. XIX, fig. 1, with PI. XX, fig. 2.) 



Locality and Stratigraphical position. — This species has been collected from the 

 Pea-grit, Inferior Oolite of Crickley, Birdlip, Shurdington, Leckhampton, Cleeve, and 

 Sudeley Hills, Gloucestershire, where it is abundant, although good specimens are rare. 

 I possess a series of all sizes, from half an inch to three inches and a half in diameter. 

 It is found likewise in the shelly freestone at Leckhampton, and I have extracted small 

 specimens from the planking beds of the Great Oolite at Minchinhampton Common. In 

 Yorkshire it is collected only from the Inferior (Great?) Oolite at Whitwell. In the 

 Pea-grit at Crickley Hill it is associated with Ammonites Murchisona, Sow., Nautilus 

 truncatus, Sow., Terebratula simplex, Buck, Terebratula plicata, Buck; and Thecidium 

 triangulares d'Orbig., is often adherent to its test. Pseudodiadema depressum, Agas., 

 Hyboclypus agariciformis, Forb., Cidaris Fowleri, Wright, Cidaris Bouchardii, Wright, 

 and Acrosalenia Lycetti, Wright, are its usual associates. 



Pygaster conoideus, Wright. PI. XIX, fig. 2 a, b, c, d, e,f. 



Pygaster conoideus. Wright, Annals and Magazine of Natural History, 2d series, vol. ix, 



p. 91, pi. 3, fig. 1. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 88. 



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



— — Desor, Synopsis des Echinides Fossiles, p. 166. 



Test pyramidal, pentahedral ; posterior border sub-acute ; ambulacral areas narrow 

 and prominent, with two rows of small marginal tubercles, and two imperfect, incomplete 

 rows within ; inter-ambulacral areas upwards of four times the width of the ambulacral ; 

 tubercles of both areas very small, and scattered without much order on the surface 

 of the plates, which are covered with minute spaced-out granules ; vent small, occupying 

 rather more than the upper third of the single inter-ambulacrum ; marginal fold acute, 

 sides of the pentahedron rising abruptly therefrom ; base flat, mostly concealed 

 by the matrix. 



Dimensions. — Height, one inch and three tenths ; antero-posterior diameter, two 

 inches and nine twentieths ; transverse diameter, two inches and four tenths. 



Description. — This very rare Pygaster is remarkable for its pyramidal form ; the 



