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



aid in the separation of the species from M. ciliata, but this 

 beak is sometimes eroded away in fossils. 



Practically all the fossil Mopalias will require re-examina- 

 tion after those of the recent fauna have become better under- 

 stood than they are at present. 



9. Mopalia hindsii (Sowerby, 1847) 

 (Plate IV. figs. 10-12.) 



1847. Chiton Hindsii Sowerby, in Reeve, Conch. Icon., v. 4, 



Chiton, sp. 67, pi. 12, f. 67a-b; detail pi., f. 67. 

 1847. Mopalia Hindsii Gray, Proc. Zool. Soc. Lond., p. 69, 



169. 

 1893. Mopalia ninscosa var. hindsii Pilsbry, Man. Conch., (1), 



v. 14, p. 296, pi. 62, f. 99-100; pi. 63, f. 57. 

 1916. Mopalia hindsii Chace, Nautilus, v. 30, p. 71 (recorded 



from Pleistocene of Deadman Id., Cal). 



Diagnosis 9 :' Valves moderately heavy, barely beaked; lat- 

 eral areas distinct, bounded in front by a low, sometimes obso- 

 lete, rather indistinctly granose rib, and behind by a much 

 weaker sutural thickening, the area between showing an inter- 

 woven basket-like pattern of varying distinctness ; head valve 

 similarly ornamented with 8 low, indistinctly granose, radiat- 

 ing ribs, showing the basket-like sculpturing between ; central 

 areas sculptured with numerous fine longitudinal riblets, either 

 weakly interlatticed, or so broken as to have a zigzag appear- 

 ance, sometimes nearly obsolete; jugal tracts with a sharp 

 longitudinal divergent ribbing, or with sculpture obsolete ; 

 sutural laminae low and broad ; sinus narrow and rather shal- 

 low ; tegmental border of median valves with a distinct, rounded 

 beak-like projection in front; teeth of head valve moderately 

 long, rather weakly vertically grooved outside; teeth of me- 

 dian valves projecting, less distinctly grooved; tail valve with 

 a single pair of lateral slits and an angular posterior sinus in 

 the articulamentum, the tegmentum rather broadly emarginate 

 above it ; mucro a little behind the center ; eaves spongy and 

 somewhat crenulate; slits 8, 1-1, 1-1. 



• Description drawn in part from recent specimens. 



