138 AXEL A. OLSSON 



Lithophaga (Diberns) plnmnla (Hanley) Plate 16, figures 1-lb 



Lithodomus plumula Hanley, 1844-, Proc. Zool. Soc. London, p. 17. Panama in Spondyli.-— 

 Reeve, 1857, Conch. Icon., vol. 10, Lithodomus, pi. 4, fig. 23. 



Modiola (Lithodomus) plumula Hanley, 1856, Cat. Recent Bivalve shells, pp. 239, 387, 

 pi. 24, fig. 23 Philippines. 



Lithophaga (Diberus) plumula (Hanley), Hertlein and Strong, 1946, Zoologica, vol. 

 31, pt. 2, p. 75, pi. 1, fig. 10.— Soot-Ryen, 1955, Allan Hancock Pacific Expedi- 

 tions, vol. 20, No. 1, p. 96, pi. 10, fig. 55. 



Shell of medium size, appearing rather stout and highest near the pos- 

 terior end of hinge, then tapering towards a bluntly rounded end. The 

 whole surface is covered by a calcareous coating which on the posterior 

 slope between the radiating sulci is much heavier, spongy or cellular, usually 

 with its sides incised by deep cuts diverging from the central axis to form 

 a crude plumose pattern likened by Hanley to that of a ruffled flower. The 

 thinner coating of lime on the ventral and anterior side is granulose and 

 wrinkled. 



The largest specimen measures: length 49.7 mm., height IS mm., 

 diameter 12.3 mm. Manta, Ecuador. 



Range — Lower California to Peru. Panama: in Spondyli (Hanley); 

 Burica Peninsula. Colombia: Gorgona Island (Hertlein and Strong). Ecua- 

 dor: Manta. 



Lithophaga (Dibenis) of. snbula (Reeve) Plate 15, figure 6 



? Lithodomus subula Reeve, 1857, Conch. Icon., vol, 10, Lithodomus, pi. 4, fig. 26, 

 Loc— ? 



Lithophaga plumula kelseyi, Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 75, 

 pi, 1, figs. 8, 9 San Diego, California. 



Lithophaga (Diberus) subula (Reeve), Soot-Ryen, 1955, Allan Hancock Pacific Expedi- 

 tions, vol. 20, No. 1, p. 97, pi. 10, fig. 56. 



There is doubt as to the name which should be applied to my shells 

 from Ecuador. They resemble L. plumula but are more delicate and the 

 posterior rib of encrustation is thinner and only slightly furrowed, not 

 developing the coarse plumose pattern of that species. They differ from 

 typical /.. kelseyi from California in the much deeper radial sulci or broad 

 furrow along the dorsal side of the central posterior zone of heavy encrusta- 

 tion, and the calcareous blades at the end of the valves are longer and 

 heavier. 



A specimen measures: length 39.3 mm., height 10.4 mm., diameter 

 11.4 mm. Manta, Ecuador, 



Range — Alaska to California and southward to Peru, Ecuador: Manta. 



Subgenus RUPIPHAGA, new subgenus 



Type species Lithophaga hastasia, new species. 



The shell, as in Lithophaga, s.s., is elongate modioliform, thin, and 

 with a light brown to nearly black periostracum, largely concealed under 

 a calcareous encrustation, thin and light on the anterior portion, 

 thickened along the posterior side so as to form a central rib bordered 

 by furrows and prolonged beyond the end of one valve only (usually that 

 of the right) in a coarse, spikelike prong or blade. Upper portion of bore, 



