231 



belongs to this species, there are iiuiications of four or five very coarse 

 radiating ribs on the posterior extremity of the sides, all of which are 

 of equal breadth. Posterior area marked by very oblique raised striaj. 



Length, thirty-foiu" millimetres : maximum height, from the centre 

 of the umbo to the ventral margin, twenty-four mm. 



Xorth side of Maud Island, a perfect but not very well preserved 

 right valve. South Island, one specimen : north side of Cumshewa 

 Inlet : two imperfect moulds of the exterior and one cast of the interior. 



This shell may be an extreme variety of the preceding species, from 

 which it differs chiefly in the peculiar ornamentation of its outer sui'- 

 face. It appears to be nearly related to the Trigonia sulcataria of 

 Lamarck,* fi-om the " Craie Chloritde " or "Upper Greensand " of 

 France, 



Trigonia Dawsoni, Whiteaves. 



Plate 31, figs. 1 and 1«. 



Trigonia Daicsord, Whiteaves. — 1878. Geological Survey of Canada, Report 



of Progress for 1876-77, p. 154. 



" Shell gently convex, compressed ; outline ovately-subtrigonal ; 

 anterior end very short, broadly rounded, as is also the ventral margin : 

 beaks elevated, recui'ved, anterior, subterminal : hinge line sloping 

 concavely downwards behind the beaks : extremity of the somewhat 

 elongated posterior end truncated rather obliquely. Surface of the 

 main body of the shell marked by about twelve curved, nodulous cosfcp, 

 all of which commence at the margin of the j^ostcrior area. The five 

 nearest the beaks ciu-ve downwards and terminate at the anterior end. 

 The middle ones, though curved, are nearly transverse, and end at the 

 centre of the ventral margin, while the last three incline decidedly 

 backwards. The posterior area is marked either by crowded, transverse, 

 regularly arranged and continuous raised striae, or by coarse, irregular 

 and broken up or angularly bent, short, tran verse folds. Iltasyouco 

 Eiver and Sigutlat Lake, frequent and well preserved." The above is 

 the original description of the species as it occurs in the volcanic por- 

 phyrites of the localities mentioned, on the main land of British 

 Columbia. 



South side of Alliford Bay : one fine specimen with the test well 

 preserved on both valves, but with a small piece broken off the pos- 

 terior end. 



The specimen from the Queen Charlotte Islands differs fi-om the types 

 of T. Dawsoni in the following particulars, though these differences 



* See D'Orbigny. Pal^ontologie Fraucaise, Terrains Cr^tacfo. Vol.'3, p. 150, 'atlas, pi. 294, 

 figs. 5-9. 



