382 PROF. S. H. REYNOLDS AND DR. A. TAUGHAN ON [Aug. 191 I, 



Chonetes cf. crassistria is figured in pi. xxvi, fig. 2 of the 

 Bristol Paper. 



This small Chonetes has the general form and convexity of 

 Ch. cf. hardrensis, but differs in the strength and spacing of its 

 ribs. There is a fine concentric striation that, in the more 

 coarsely-ribbed forms, is as obvious as in Ch. stoddarti. 



Occurrence. — Common in K and Z l of many localities in the 

 South-Western Province, but rare at Burrington. 



Chonetes cf. hardrensis Phill., Dav. (' Dav.' pi. xlvii, fig. 22.) 



Shell small, convex, non-transverse, and finely ribbed, with a 

 small number of hinge-spines. 



Distinguished with difficulty from small Chonetes that are 

 abundant in Upper D of the North of England and Scotland. 



At Burrington, as in the South-Western Province generally, this 

 species crowds the surfaces of beds in Z 1 and occurs more rarely in 

 the Upper Tournaisian ; it is practically absent from the Visean. 



Chonetes cf. lagtjessiana is figured in pi. xxvi, fig. 1 of the 

 Bristol Paper. 



Shell flattened, transverse, rectangular, finely and closely ribbed. 



Cardinal region almost perfectly flat ; the rest of the surface 

 very gently flexed. Cardinal spines numerous. 



Occurrence at Burrington. — Abundant at certain levels 

 in K and common in Z x . 



II. The large Chonetes of the Upper Tournaisian: — 



Chonetes cf. comoides of the Bristol Paper includes two distinct 

 forms, agreeing in large size and massiveness with Chonetes 

 comoides Sow. 



(1) A large Productoid form, excusably confused with Productus 

 giganteus. 



The muscular field of the convex valve is that of Chonetes, 



and not of Productus ; there are no accessory adductors as in 



Daviesiella. 



The development of this giant Chonetes seems to have been 



carried out within the South-Western Province, for there is 



continuous increase in size and convexity (but essential agreement 



in other traits) onward from Z 1? where the gens is first recognized. 



The Z ± mutation is rare, but conspicuously larger than the 



abundant Ch. cf. hardrensis ; it is essentially distinct in form from 



Ch. cf. laguessiana. 



There is of necessity some difficulty in unravelling the history 

 of the gens below Z , for further diminution of size would result 

 in a small form so like Ch. cf. hardrensis as to require most minute 

 discrimination. 



Occurrence at Burrington. — Common at the bottom of 

 the C T dolomite, and at the same level in the South-Western 

 Province generally. 



