206 



the transverse ridges are not imbricated, but smoothly rounded. The 

 character of the hinge of the dorsal of L. Escasoni is quite different from 

 Obolus. The area is quite low and the posterior end of the valve rounded 

 steeply down ; whereas in Obolus the area is high and that end of the 

 valve flat. 



Also in the ventral valve the scar of the central muscles is triangular 

 as in Lingulella, not rounded in at the sides as in Obolus. For these 

 reasons, if L. (?) Escasoni is to be included in Westonia, to me the sub- 

 genus would seem to be related to Lingulella rather than to Obolus. 



The ornamentation of peculiar transverse waving ridges, however, is a 

 convenient common character that unites a number of forms and so is 

 useful as a feature held in common, and due to a like origin, in these 

 beautifully ornamented shells. 



The Canadian species being of the Peltura Zone is a little older than 

 O. (L.) aurora, which being associated with Dicellocephalus Minnesotensis 

 should be within the Tremadoc Zone. 



WESTONIA ESCASONI. PI. XVI., figs. 1 a-h. 



Nat. Hist. Soc. of N. B. Bull. vol. iv, p. 270, pi. v, figs 1 a-c Matt. 



" Corneous, but having a thin outer calcareous layer. The inside of 



described the edges of the valves is flattened, 

 ventral valve. 



Ventral valve ovate, pointed at the apex, somewhat elevated from the 

 umbo, along the axial line. Interior. Cardinal area short, traversed by 

 a depressed pedicle groove. The cavity between the umbo has impres- 

 sions of two small, cardinal muscles, from which radiate two grooves, 

 The ventral bordered outside by ridges that separate the lateral muscle scars from the 

 visceral cavity. The print of the central muscle is oval or lenticular and 

 transverse to the axis of the valve ; it is divided lengthwise, half way, by 

 a septum ; the posterior half of the scar is again divided by a faint ridge 

 at right angles to the septum named. The "1" laterals are small trian- 

 gular imprints in front of the outer part of the central muscles. In some 

 valves the paired scars of the "k" laterals at the middle of the central 

 group are small, and behind them extending toward the umbo is a sharp 

 furrow enclosed between narrow ridges ; in others they are wider and the 

 ridges are not preserved. The grooves of the lateral muscles are discern- 

 able near the hinge on each side; the transmedian ("i") being external 

 and on the inner edge of the flattened margin of the valve; the("j") 

 laterals are on the slope of the valve within the flattened margin. 



