Vol. 67.] THE CARBONIFEROUS SUCCESSION IN GOWER. 561 



Chonetes. 

 Chonetes sp. (PI. XLI, figs. 3 a & 3b.) 



Circumference rectangular, with nearly square cardinal angles. 

 Ribbing fine and close-set. 



In the pedicle-valve the form is flattened-convex, with the 

 maximum rise at half-way across the valve. The strong growth- 

 halt and the thickened marginal band below it cause a deep 

 marginal depression in the cast. A shallow marginal median sinus 

 and a corresponding median inflection of the circumference are 

 occasionally developed. 



This species is very common at certain levels in D 23 of 

 Oystermouth and Bishopston in Gower. It also occurs abundantly 

 farther west in the South- Western Province, at Ragwen Point 

 near Pendine, at approximately the same level (namely, Horizon e). 



Daviesiella. 



The essential character of Daviesiella Waagen as exhibited in 

 the genotype D. llangollensis (Dav.) is the presence of an additional 

 pair of adductors in the large valve ('Davidson' pi. lv, fig. 9 — 

 scars lettered C). 



The large Productoid Chonetes from C — Chonetes cf. comoides — 

 has no additional adductors ; whereas, in the Productoid Chonetes 

 from D — Chonetes (Daviesiella) aff. comoides — these scars are very 

 conspicuous. 



STROPHOMENIDS. 



' Orthotetes ' cf. CRENISTRIA (Phill.). (PI. XLI, fig. 4.) 



Description. — Hinge-line less than the width of the shell; 

 area asymmetrical. Brachial valve strongly convex as a whole, 

 but flattened in the neighbourhood of the beak. 



The radial ornament is strong and markedly periodic. 



The concentric fine, close-set growth-lines produce a delicate 

 1 crenistriation ' on the ribs and a reticulation of the narrow flat 

 interspaces ; there are a few well-marked growth-halts. Dental 

 plates on a simple Strophomenoid plan. 



Comparison. — In area and ornament this form approaches 

 very closely to 0. crenistria ; by its marked convexity l and more 

 strongly periodic ribbing it is easily distinguished. 



This form is not uncommon in the Oystermouth beds (D 2 1 3 ). 



1 The figured specimen is from thin shales and is crushed fiat; specimens 

 showing the strong convexity of the brachial valve were, however, obtained. 



