262 University of California Publications in Geology [Vol. 9 



PAGE 



Spisula hemphillii (Dall) 287 



Spisula occidentalis (Gabb) 288 



Spisula abscissa (Gabb) 289 



Spisula albaria (Conrad) 290 



Spisula albaria (Conrad) var. ramonensis, n. var 291 



Spisula selbyensis, n. sp 292 



Spisula planulata (Conrad) 293 



Spisula merriami Packard 294 



Spisula acutirostrata, n. sp 295 



Spisula brevirostrata, n. sp '. 296 



Subgenus Symmorphomactra Dall 297 



Spisula falcata (Gould) 297 



Subgenus Cymbopliora Gabb 298 



Spisula ashburnerii (Gabb) 298 



Spisula gabbiana (Anderson) 299 



Spisula cbicoensis, new name 300 



Subgeneric Position Uncertain 301 



Spisula callistaeformis Dall 301 



Spisula coalingensis (Arnold) 301 



Spisula lenticularis (Gabb) 302 



Spisula sisquocensis Arnold 302 



Spisula tejonensis, n. sp 303 



Genus Mulinia Gray 



Mulinia densata Conrad 304 



Mulinia densata Conrad var. minor Arnold 307 



Mulinia alta (Weaver) 307 



Mulinia undilifera (Weaver) 308 



Mulinia landesi (Weaver) 309 



Mulinia pabloensis, n. sp 309 



Generic Position Uncertain 310 



Mactra(?) gibbsana Meek 310 



Mactra(?) montereyana Arnold 311 



Mactra(?) stantoni Arnold 311 



Mactra(?) tenuissima Gabb 312 



Spisula (?) weaveri Packard 313 



Species Not Valid 



Mactrat?) gabiotensis Conrad 313 



INTRODUCTION 



Although a considerable number of species belonging to the sub- 

 family Mactrinae have been described from the Pacific Coast region 

 of North America, the taxonomy and the phylogeny of the group 

 have been but imperfectly understood. The existing situation is due 

 largely to great individual variation in the superficial specific char- 

 acters of the shell. As a consequence of our lack of understanding 

 of the group, there has been much confusion regarding the geologic 

 range of certain mactrine species. 



