446 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



10. Mopalia acuta (Carpenter, 1855) 

 (Plate V, figs. 10-11.) 



1855. Chiton acutus Carpenter, Proc. Zool. Soc. Lond., 1855. 

 p. 232. 



1864. Mopalia acuta Carpenter, Rep. Brit. Assoc. Adv. Sci.. 

 1863, p. 527, 648. 



1893. Mopalia muscosa var. acuta Pilsbry, Man. Conch., (1), 

 v. 14, p. 297, pi. 64, f. 75-81. 



1917. Trachyderniou dcntiens Chace, Lorqninia, v. 2, p. 30 

 (not Chiton dentiens of Gould ; recorded from Pleis- 

 tocene of Santa Monica, California). 



Diagnosis: Valves small to moderate in size, rather deli- 

 cate; sculptured in similar fashion to M. lignosa, but the sutural 

 rib in valves i-vii typically ornamented by series of delicate 

 denticles; sutural laminae short and wide; sinus narrow and 

 rather shallow ; tegmental border of median valves weakly 



Fig. 9. Mopalia acuta (Carpenter). Anterior elevation of valve illus- 

 trated in Plate V, figs. 10-11; camera outline. 



false-beaked in front ; teeth rather short, only moderately pro- 

 jecting; tail valve with a single pair of lateral slits, one or more 

 of which may be duplex, and a small posterior sinus, often 

 showing a small tooth at the apex; eaves spongy; slits 8, 1-1, 

 1-1. 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Nob Hill Cut, 

 San Pedro, California ( !). 



Upper San Pedro Series — Long Wharf Canyon, Santa 

 Monica, California ( !) ; Los Cerritos Hill. Long Beach, Cali- 

 fornia ( !). 



Formation doubtful — Deadman Island, San Pedro, 

 California ( !). 



Living: Monterey, California (!) to Todos Santos Bay, 

 Lower California ( !) 10 . 



10 The record by Baker from Ellamar, Alaska, surely requires confirmation. 



