74 



Geologists still differ slightly with, respect to the number of 

 divisions into which the Oolitic and Liassic deposits should be 

 separated; thus, for example, the Fuller's earth, Stonesfield 

 slate, Bradford clay, Forest marble, and perhaps one or two 

 others, are local and unimportant divisions when compared with 

 such divisions as the Inferior Oolite, Great Oolite, Oxford Clay 

 and Kimmeridge. Some geologists desire to omit these minor 

 divisions; others, on the contrary, would subdivide the whole 

 system into a great number of zones characterised by the 

 presence of certain species of Ammonites, and although this 

 mode of proceeding may have its advantages as a matter of 

 detail, our knowledge as to the real value of all these zones is 

 not yet so far advanced as to warrant us following them in the 

 general grouping of the Brachiopoda scattered throughout the 

 system. In nature we find no hard lines of demarcation between 

 the divisions which we are obliged to adopt in order to be able 

 to define their respective positions. Thus the Rhaotic would 

 connect the Triassic series with the Liassic ; the Midford sands, 

 E. cynocephala bed, &c., form the passage connecting the 

 Liassic with the Oolitic series of deposits. 



It was during the deposition of the Middle Lias and Inferior 

 Oolite that both species and specimens of Brachiopoda abounded 

 in the Jurassic rocks of Great Britain. As many as fifty-nine 

 species and named varieties have been recorded from the Middle 

 Lias, and about sixty-five from the Inferior Oolite. 



No. 1. TEREBRATULA PEROVALIS, Sow. Min. Con., Plate I., fig. 

 1, 2; Plate III., fig. 1. 



TEBEBBATULA PEEOVALIS, Sow. Min. Con., vol. v., p. 51, tab. 436, 

 fig. 2, 3; and Var. Ampla (Buckman), pi. i., fig. 1, 2, Pro- 

 ceedings of the Somersetshire Archceological and Natural History 

 Society, vol. xx., 1874. 



This is -the largest species of Brachiopoda with which we are 

 acquainted from the Oolite rocks of Great Britain, some speci- 

 mens having exceeded three inches in length by two inches, and 

 three or four lines in breadth, 



