I 916 ] Packard: Mesozoic and Cenozoic Mactrinae 293 



pressed; left cardinal high, arms of nearly equal length, not widely 

 diverging; this tooth extends from the dorsal to the ventral margin 

 of the hinge plate; ventral sinus very restricted; laterals long, low, 

 round-topped, arising from the ventral margin of the plate ; base 

 of the anterior lateral not reaching to the cardinal arm; right car- 

 dinal well developed, with a heavy anterior arm, which is closely 

 appressed to the margin of the shell ; posterior arm also heavy, 

 reaching to the ventral border of the plate ; anterior ventral lamina 

 long, in the same plane with, and joining the anterior cardinal arm 

 by a low ridge. The dimensions of the type are : length, 29 mm., 

 convexity, 10 mm. 



This species resembles 8. albaria in general outline, but it differs 

 from that species in that it is generally more inequilateral and more 

 elongate, with a narrower hinge plate, and more compressed left 

 cardinal. The length of the laminae and the close relationships 

 between the anterior ventral lamina and the cardinal arm also 

 characterize this species. 



The shape of this species is exceedingly variable. The beaks 

 are in some specimens anterior to the middle of the shell, while in 

 others from the same collecting locality they are posterior to that 

 line. This variation has already been discussed at some length in 

 another portion of this paper (page 268). 



The type was obtained from University of California Locality 

 1352. This locality was described by J. C. Merriam under number 

 360 as follows: "One-third of a mile south-west of Vallejo Junc- 

 tion, in a bluff close to the railroad track at the lowest Miocene con- 

 tact with the Martinez, Napa sheet." 



Occurrence. — Miocene : Monterey group, Area montereyana zone. 



SPISULA PLANULATA (Conrad) 

 Plate 16, figures 3a, 3b and 3c 

 Mactra planulata Conrad, Jour. Acad. Nat. Sci. Phila., vol. 7, pt. 2, p. 240, 

 1837; (not M. planulata of Carpenter nor Standella planulata of Gabb, 

 Cooper nor Stearns). 23 



Spisula planulata (Conrad), Conrad, Am. Jour. Conch., vol. 3, appendix, 

 p. 45, 1868; Dall, Nautilus, vol. 8, p. 40, 1894; Proc. Royal Soc. Canada, 2d. 

 ser., vol. 1, p. 48, 1894. 



The general shape of this shell is somewhat like that of 8. falcata, 



23 These authors confused several species, notably S. albaria, S. planulata 

 and 8. voyi, therefore their citations have but little value. 



