232 



are obviously not of spoeitic importance. In the AUiford Bay shell 

 the number of curved nodulous ribs on the sides of the valves is at 

 least eighteen : its posterior area, in addition to the transverse lines 

 which cover its surface, is marked by three equidistant, curved, longi- 

 tudinal rows of nodules or nodulous ridges, in each valve, which extend 

 from the beaks to the posterior margin. The lower row of nodules 

 which bounds the posterior area externally, is prominent and com- 

 posed of comparatively large nodules, but the two upper nodulous 

 ridges are not so prominent and are composed of much smaller nodules. 

 It is not imjjrobable that T. Daivsoni may be only a variety of the T. 

 Montanaensis of Meek,* but for the present it is thought prudent not to 

 unite the two forms under one name, for the following reasons. In T. 

 Montanaensis the front margin of the valves is said to be ornamented by 

 a transverse row of nodules which latter are " larger than the others and 

 are ranged in a vertical row of strong nodules, which form a conspicu- 

 ous feature of the shell, "f and its posterior area is described as "marked 

 only by numerous, distinct, nearly vertical lines of growth. "J There 

 is no such vertical row of large nodules on or near the anterior margin 

 of any of the specimens of T. Dawsoni, and on the posterior area of 

 the Queen Charlotte Island variety of that species the transverse raised 

 lines, as already stated, are crossed by three nodulous ridges or longi- 

 tudinal rows of isolated nodules. 



NucuLA (Acila) truncata, Gabb. 



Nucula truncata, Gabb. — 1864. Palseontology of California, Vol. I, p. 198, pi. 26. 

 figs. 184 and 184 a, b. 



Bear Skin Bay and Bay east of Alliford Bay, in Skidegate Inlet : 

 one characteristic specimen from each of these localities. 



Nucula solitaria, Gabb. 

 Plate 31, figs. 3 and 3a. 



Nucula solitaria, Gabb. — 1869. Palseontology of California, Vol. 2, p. 197, pi. 



32, fig. 94. 



South side of Alliford Eay : nine good casts of both valves with ])or- 



* See Dr. C. A. White's Contributions to Paljeontology, Nos. 2-8. Washington. 18S0. P. 147, 

 pi. 38, fig. 2a. 

 t lb., page 146. , 



t Jb., page 146. 



