288 FOREIGN JURASSIC PYGASTERS. 



Dimensions. — Height, six tenths of an inch ; transverse diameter, one inch and a half; 

 antero- posterior diameter, nearly one inch and a half. 



Formation. — Corallien, " Couches superieures de l'etage corallien, et recueillis dans les 

 carrieres de Vauligny pres Tonnerre (Yonne)." Cotteau. " Dans un 

 banc a coraux du Portlandien, a Reedersdorf (Haut-Rhin)." Agassiz. 



Collections.— M. Rathier, M. l'abbe Bellard, M. Gressly, M. Cotteau. Rare. 



Pygaster patelliformis, Agassiz. Echinoderm. Foss. Suisse, tabl. 13, figs. 1 — 3. 



Desor. Monog. des Galerites, tabl. 11, figs. 11 — 13. 



Test thick, hemispherical, more or less depressed ; circumference sub-pentagonal ; 

 tubercles large, equal-sized, and arranged in regular rows ; ambulacra with four rows of 

 tubercles ; inter-ambulacra four times the width of the ambulacra, with fourteen rows of 

 tubercles ; all the tubercles surrounded by small granules ; anal opening large, pyriform, 

 contracted above, wide below, occupying two thirds the length of the area; mouth 

 opening large, peristome deeply notched. 



Dimensions. — Height, one inch and a quarter ; transverse and antero-posterior diame- 

 ters, three inches. 



Formation. — " Kimmeridge de Lauffon dans la vallee de la Birse (Berne)." Agassiz. 

 Collections. — Museum of Neuchatel, M. Gressly. Very rare. 



Pygaster dilatatus, Agassiz. Syn. Pygaster umbrella, Agassiz. Echinoderm. Foss. 



Suisse, part. l e , tabl. 13, figs. 4 — 6. 

 Pygaster umbrella, Desor. Monogr. des Galerites, 

 tabl. 12, figs. 4—6. 



This is the urchin which was described by MM. Agassiz and Desor in their respective 

 works as the type of Pygaster umbrella. In their ' Catalogue raisonne/ however, it is 

 separated from P. umbrella of the Coral Rag, under the name P. dilatatus, with this 

 remark—*" Se distingue du P. umbrella par son bord plus tranchant et sa forme plus 

 dilatee." The original specimen is an interior mould ; M. Gressly has, however, found one 

 with a portion of the test preserved. The fragment of the test is very thick, and has large 

 tubercles, disposed nearly as in P. patelliformis. The general form of the mould, and 



