PERNA. 



S!l 



Affinities. — The forms found in the Lower Greensand of England which had 

 been referred to Perna Mulleti by earlier writers were regarded as distinct by 

 Pictet and Oampiche, and were named by them Perna Forbesi. They considered 

 that the latter were distinguished by the more prominent folds, the shorter and 

 more deeply concave anterior margin, and the longer posterior wing. An 

 examination of a number of specimens shows that these characters are variable, 

 and I am led to agree with Wollemann in thinking that the forms described by 

 Pictet and Campiche cannot be regarded as more than varieties of a variable 

 species. 



I<i<; l.i. I'mn t Miillrh, l><' .Ii;i\r ,. I„ nvcr < iivensand ( P .nut-bed), Sand, iwn. Sedgwick Museum. L 

 valve x f. (The posterior whig is broken. Forbes gives a figure of a specimen iu which the wiu«. 

 perfectly preserved. ) 



e specimens 



Perna Mulleti is the type of Fischer's section Mulletia. 



Type. — From the Neocomian of Vendeuvre. I have not seen tl; 

 figured by Forbes. 



Distribution. — Perna-bed of Atherfield and Sandown. Atherfield Beds of 

 Haslemere, Peasmarsh, Shalford, Redhill, Sevenoaks, and Hythe. Hytlie Beds 

 of Hythe (fide Topley). Lower Greensand of Potton and Upware. Teal by 

 Limestone (zone of B. brunsvicensis) of North Willingham. Speeton Clay of 

 Speeton. 



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