290 FOREIGN JURASSIC PYGASTERS. 



Pygaster macrocyphus, Wright, nov. sp. Davidson's MSS., pi. 2, figs. 1, 2, 3. 



Test thick, large, sub-pentagonal ; upper surface convex, or more or less depressed ; 

 base concave ; ambulacra narrow, with two irregular rows of small marginal tubercles, and 

 two short rows, equally irregular, internal to them, which disappear from the upper 

 two thirds of the* areas ; inter-ambulacra five times the width of the ambulacra ; each of 

 the plates near the border supports about seven unequal-sized tubercles ; those repre- 

 senting the primary rows are larger than the others ; the tubercles, however, are in 

 general large, and very irregularly disposed ; the inter-tubercular surface of the plates is 

 covered with an abundance of miliary granules ; the bosses of the tubercles are prominent, 

 and surrounded by ring-like areolas, and the granules form circles around each ; there is 

 a median depression in the centre of the upper part of the areas ; the anal opening is 

 small in proportion to the size of the urchin, and occupies nearly the upper two thirds of 

 the area ; it appears to have had a pyriform shape, much of the upper surface of the test 

 is broken in my specimen, so that its precise form is indeterminable ; base concave ; 

 mouth opening small, one sixth the diameter of the test ; peristome deeply notched, 

 lobes equal. 



Dimensions. — Height, one inch and a half; transverse diameter, four inches and a 

 half. 



Formation. — Kimmeridge clay, from a cliff between Boulogne-sur-Mer and Portel. 

 Very rare ; I only know two specimens. 



Collections. — Thomas Davidson, Esq., F.R.S. The specimen in my collection was 

 found by M. Bouchard -Chantereaux in the same rock and locality, 

 and was generously given me by that gentleman for this work. 



Pygaster tenuis, Agassiz. Echinoderm. Foss. Suisse, p. 83. 



Desor. Monogr. des Galerites, tabl. 12, figs. 1 — 3. 



" A very large, sub-pentagonal, depressed species, with small and numerous tubercles, 

 twenty rows in the inter-ambulacral areas, and six in the ambulacral areas, which are not 

 very regular. This species is distinguished by its very thin test. 



" Formation. — Corallien inferieur (Terrain a chailles) de Fringeli, Canton de Soleure. 



" Collection. — M. Gressly. Very rare." Desor. 



