ALBIAN FOSSILS DISCOVERED AT OKEFORD FITZPAINE. 85 



summits obtusely angulated and raised slightly above the general 

 periphery of the shell ; there is no indication of a distinct byssal 

 sinus beneath either of the anterior ears; height greater than 

 length ; test fragile. 



Dimensions Height = 14 1 



_, } Millimetres. 

 Length = 12'5j 



Another valve, rather larger, has a smooth shining surface, 

 through which can be seen a series of obscure, closely-set, fine 

 concentric lines ; this represents an upper or left valve. The 

 largest specimen in the collection has a height and length respec- 

 tively of 55 and 50 millimetres ; it shows the transverse ridges 

 for articulation purposes in the auricles, and the central ligamental 

 fossette is also obscurely seen. 



Interiors of this species observed in specimens from other 

 localities show a comparatively smooth surface with no elevated 

 radial ribs. 



It is difficult to recognise this and similarly-formed pectinoid 

 shells under the name of Pecten if we would restrict that genus in 

 its meaning to such types as Pecten maximus or P. Islandicus. I, 

 therefore, follow Stoliczka in adopting Meek's Syncyclonema * of 

 1864 to include those shells which exhibit such characters as 

 are here indicated. This genus, founded by its author for the 

 reception of a small Cretaceous species known as Pecten rigida 

 (Hall and Meek), was described as follows : " Shell small, 

 compressed, nearly equivalve, vertically ovate, the height being 

 greater than the transverse diameter ; hinge line very short ; ears 

 very small, the anterior being larger than the other ; margins 

 closed all round ; no defined byssal sinus in either valve ; surface 

 onl}' showing concentric strise, and sometimes stronger, regularly- 

 defined concentric ridges on the right valve." Some authors have 

 regarded Syncyclonema as synonymous with Pseudamussium, but 

 this latter genus, as generally understood, appears to include a 



* Smithsonian Check-List, North American Cretaceous Fossils, 1864, 

 p. 7 ; Kept. Invert. Cret. and Tert. Fossils, Upper Missouri, United 

 States Geol. Surv. Terr , 1876, p. 26. 



