Clark: The San Lorenzo Series of Middle California 133 



practically flush with the anterior edge of the shell, while on P. peck- 

 hami this edge is considerably back of the edge of the shell ; also on 

 the former the byssal notch is deeper than on the latter. 



Family Anomiidae 

 Genus ANOMIA Muller 

 ANOMIA INCONSPICUA, n. sp. 

 Plate 13, figures 19 and 20 

 Type specimen 11205, Coll. Invert. Palae. Univ. Calif., loe. 1131 

 Shell small, thin, subcircular and somewhat variable in outline ; beaks incon- 

 spicuous, subcentral in position, on some specimens slightly twisted but on others 

 not; left valve convex; right valve flat, with a large byssal notch. Surface 

 smooth except for rather heavy, irregular incremental lines. Muscle area, as 

 seen on left valve, with one fairly large, distinct scar which is slightly posterior 

 to the beak; other scars indistinct. Hinge line very thin, with a small, deeply 

 sunken resilifer. 



Dimensions. — Type specimen: (left valve) height, 4 mm.; length, 4.5 mm.; 

 paratype (a right valve): height, 4.5 mm.; width, 4.5 mm. 

 Occurrence. — University of California locality 1131. 



This species appears to be quite distinct from anything described 

 from the West Coast. Possibly the form that is nearest is Anomia 

 linatvla Dall, 109 from which it differs in being much smaller, in the 

 hinge not being so heavy, and in lacking the faint radiating lines seen 

 on the latter. 



Family Mytilidae 



Genus MODIOLUS Lamarck 

 MODIOLUS KIRKERENSIS, n. sp. 

 Plate 9, figure 8 



Type specimen 11121, Coll. Invert, Palae. Univ. Calif., loc, 3081 

 Shell medium in size ; base straight or nearly so, on some specimens being 

 slightly concave; anterior end rather strongly produced; posterior margin angu- 

 lated back of middle of shell ; posterior to this the margin slopes in rather 

 obliquely to the posterior end, which is regularly rounded but not very wide. 

 Unibones prominent; umbonal ridge distinct but not extending to the posterior 

 end of the shell. Surface rather acutely arched in the anterior third of the 

 shell but gently rounded near the posterior end ; anterior slope steep, slightly 

 excavated in front of the umbonal ridge. Posterior slope not so steep as 

 anterior ; in the vicinity of the posterior angle the surface is depressed or flat- 

 tened, giving the shell an alate appearance similar to that seen on Modiolus rectus 

 Conrad, a common Recent West Coast species. Surface, except for an elongated, 



109 For original description of A. linatula, see Proc, U. S. Nat, Mus., vol. 1, 

 p. 15, 1879, and Trans. Wagner Free Inst. Sci., vol. 3, pt, 4, p. 785, pi. 35, fig. 19, 

 1898. 



