484 



CALIFORNIA ACADEMY OF SCIENCES 



[Proc. 4th Ser. 



34. Callistochiton crassicostatus Pilsbry, 1893 

 (Plate XIII.) 



1893. Callistochiton crassicostatus Pilsbry, Man. Conch., (1), 

 v. 14, p. 264, pi. 58, f. 1-6. 



1917. Callistochiton crassicostatus Chace, Lorquinia, v. 2, p. 

 30 (recorded from Pleistocene of Santa Monica, 

 Cal.). 



1919. Callistochiton crassicostatus Chace and Chace, Lor- 

 quinia, v. 2, p. 42 [2] (recorded from Pleistocene 

 of Pt. Fermin, Cal.). 



( . Chiton Umbriatus of various authors, but not of Sow- 



erby, teste Pilsbry.) 



Diagnosis: Valves small, thick, massive, well arched, scarcely 

 angled ; side slopes strongly arcuate ; lateral areas raised into a 

 strong, thickened rib, coarsely granulated and cut by one or 

 more shallow radial sulci ; head valve typically with 7 massive, 

 radial ribs, each with a shallow median sulcus and sometimes 

 others toward the base, the interspaces concentrically decus- 

 sated; central areas strongly longitudinally ribbed. 7-12 ribs 



Fig. 10 



Fig. 10. Callistochiton crassicostatus Pilsbrv. 

 valve illustrated in Plate XIII, figs. 6-7. 



Anterior elevation of 



on a side, distinctly converging on the jugum, the interspaces 

 finely latticed across; tail valve elevated, flattened above, the 

 mucro increasingly posterior with growth, the slope behind it 

 becoming almost vertical ; sutural plates low, distinctly con- 

 nected across the shallow sinus; teeth short, scarcely project- 

 ing in valves i-vii, very short and thick in valve viii ; eaves solid ; 

 slits 9, 1-1, 14 to 18. ' 



Recorded Range: 



Pleistocene: Lower San Pedro Series — Chiton Bed, 

 Point Fermin, California (Chace and Chace, !) ; Nob Hill Cut, 

 San Pedro, California (!). 



