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tions, about 60 on each valve. Since the intercalation of plications 

 among those which may be regarded as primary is almost confined 

 to the posterior third of the shell, it is evident that it is not the 

 larger size of this shell, compared with Zygospira recurvirostra, 

 which gives this Catazyga the appearance of having more plica- 

 tions than the latter species. Compared with typical Catazyga 

 iiphami, the specimens from High Bridge are broader, less elongate 

 anteriorly, with a broad shallow depression on the anterior half of 

 the pedicel valve, and a corresponding low elevation on the brachial 

 valve. Since the absence of the sinus in the pedicel valve is char- 

 acteristic of typical Catazyga uphami, the specimens from High 

 Bridge may be regarded at least as a variety. 



Catazyga headi — schuchertana, Ulrich. 



(Plate II, fig. 3; Plate III, figs. 11 A. B. C.) 



Catazyga headi was described by Billings from loose blocks of 

 limestone, more or less erratic, found on the south side of the St. 

 Lawrence river, opposite Three Rivers, seventy miles southwest of 

 Quebec. The types described by Billings no longer can be identified 

 among the material preserved in the Museum of the Canadian 

 Geological Survey, but specimens collected by Whiteaves from the 

 type locality are at hand and may be regarded as replacing the 

 types. These specimens present the following characteristics. 



Beak of pedicel valve slightly compressed laterally, the com- 

 pression extending anteriorly as a faint elevation, the sides of 

 which diverge at angles of about 12 degrees with the median line. 

 Anterior to the center of the valve, the median part of this faint 

 elevation is slightly depressed, forming a very faint and rather 

 broad median depression. The brachial valve has a very faint 

 median depression near the beak. Toward the anterior part of 

 the valve there may be a faint median depression, a faint elevation, 

 or neither, showing that these features can not be regarded as 

 specific characteristics. The general appearance of the shell is well 

 represented by the figures accompanying the original description. 

 The lateral outline varies. The lateral outline usually is slightly 

 straightened, even in the broadest specimens, but some specimens 

 are distinctly compressed laterally, and then have a distinctly elon- 

 gate appearance, resembling the form figured by Billings as variety 

 horealis. With an abundance of material at hand, it appears impos- 



