FOREIGN JURASSIC PYGASTERS. 289 



the shape of the anal opening, which is pyriform, likewise resemble that species. M. 

 Desor, in his ■ Synopsis,' remarks — " Grande espece subpentagonale, etalee, a bord plus 

 aminci que dans aucune autre espece." It is probable that P. patelliformis and 

 P. dilatatus may be different conditions of the same species, as they are both Kimmeridge 

 forms. 



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



Formation. — "Kimmeridge du Jura Soleurois, carriere de Greifel, vallee de la Birse 

 Canton de Berne." Agassiz. Very rare. 



Collection. — M. Gressly. 



Pygaster pileus, Agassiz. Syn. Pygaster pileus, Cotteau. Etudes sur les Echinides 



Foss., pis. 29 and 30. 

 Pileus hemispharicus, Desor. Syn. Echinod. Foss., 

 tabl. 22, fig. 6. 



Test large, sub-pentagonal ; upper surface sub-conical ; base flat or sub-concave ; 

 ambulacra convex and prominent, with six rows of small, irregularly disposed tubercles ; 

 inter-ambulacra wide, with numerous small tubercles disposed partly in single, and 

 partly in double, horizontal rows ; middle of the areas depressed, and deprived of 

 tubercles ; anal opening pyriform, situated in the lower half of the single inter- 

 ambulacrum ; between the apex of the vent and apical disc the test is entire, so that 

 a large triangular space exists in this species, filled with the plates of the test, not found 

 in other Pygasters, in all of which, with this exception, the discal opening and vent 

 conjoin ; mouth small, situated in a deep depression in the centre of the under surface. 



Dimensions. — Height, one inch and three quarters ; transverse and antero-posterior 

 diameters, four inches. 



Formation. — " Coral-rag inferieur ; dans les couches blanches et pisolithiques de 

 Coulanges-sur-Yonne et de Chatel-Censoir ; calcaire a chailles de 

 Druyes." Cotteau. 



Collections. — Museum d'histoire naturelle de Paris, M. Salomon, M. Cotteau. Very 

 rare. Plaster mould in my cabinet. 



In consequence of this Pygaster having the anal opening in the lower part of the 

 inter-ambulacrum, and a considerable portion of the test between its apex and the disc, 

 M. Desor has erected it into a new genus, under the name Pileus hemisphcericus. 



