FAUNAL SUCCESSION OF THE UPPER BERNICIAN 635 



from the rest of the shell, and are decorated by concentric 

 wrinkles which extend on to the body of the shell. The spines 

 are few in number. (Plate xvii., fig. i). 



The Latissimoid Group. — The latissimoid Froduc ft xezch. 

 their numerical maximum and acme of specialization in the 

 Middle and Upper Limestones, occurring in great numbers 

 and possessing very wide range of variation, a range which 

 has the typical P. latissinms as one extreme and circular and 

 globose forms as the other. The most characteristic and 

 abundant form is Productus /?. 



Productus p. — The variety is more oval in shape and is 

 flatter than Sowerby's type of P. latissinms, but it agrees with 

 Davidson's description of the species in the gradual passage 

 of the body of the shell into the auriculate expansions. The 

 shell, being finely striated, has on that account a smooth 

 appearance, and is ornamented with sparsely distributed but 

 stout and erect spines. (Plate xvii., fig. 2). 



The Semireticulate Group. — A variant agreeing with 

 P. ptigilis (Phillips) in respect to strong ridges upon the 

 pedical valve towards the margin and the prominent spines it 

 bears, is the prevailing type of the semireticulate Producti 

 found in the Bernician sequence. 



P. antiquatus is common in the Fourlaws Limestone and 

 Redesdale Ironstone Shale. 



foraminifera. 



Saccammina carteri, Brady (Ann. and Mag. Nat. History, 

 series ii., vol. vii., p. 177, pi. x. ; Pal. Soc, vol. 34, 1876). — 

 This small fossil is of the greatest importance as far as 

 Northumberland is concerned, and was long used by the 

 quarrymen as an index of horizon before the principles of 

 zoning were understood. It is found in small quantity in 

 most of the Lower and Middle Limestones, but is abundant in 

 the Four Fathom and the Six Yards or Acre Limestones. 

 The " spotted band," as the thin horizon is called at which it 

 occurs in great quantity, migrates from the Four Fathom to 

 the Acre Limestone northwardly. (Plate xviii., fig. i). 



