332 CALIFORNIA ACADEMY OF SCIENCES. 



only slightly appressed, distinct; aperture subtriangular; outer lip thin, slighdy bowed anteriorly; 

 umbilicus large, deep, surrounded by callous extension of the columella. 

 Dimensions. — Alt. 32 mm.; lat. 40 mm. 



Described from a living specimen. 



Found in upper San Pedro series at Deadman Island. Found also in the 

 Pleistocene at Pacific Beach, San Diego. 



Living. — Santa Barbara to San Diego (Cooper). 



Pleistocene. — Santa Barbara (Cooper): San Pedro; San Diego (Arnold). 



Genus Margarita Leach. 



Shell thin, globular-conical, umbilicated; whorls rounded, smooth; aperture rounded, 

 pearly; lip sharp, smooth. 



Margarita helicina Fabr. is a characteristic species. 



386. Margarita optabilis Carpenter, var. knechti, var. nov. 



Plate V, Fig. 14. 



Gibbida optabilis Cpr., Brit. Assn. Rept., 1863, p. 653. 



Shell small, conical, thin; turbinated apical whorls; whorls five; upper whorls rather angular, 

 slightly tabulated above; body-whorl rounded, slightly angulated at base; two prominent spiral 

 ridges, one at angle of whorl, the other near anterior margin; between these two ridges is a slightly 

 concave surface sometimes ornamented with faint spiral ridges; oblique incremental lines quite 

 prominent; suture impressed and distinct; base of body-whorl only slightly convex, and ornamented 

 by five spiral ridges; umbilicus large, deep, effuse, smooth; aperture subrotund; inner lip incrusted 

 and projecting slightly over umbilicus. 



Dime7isions . — Alt. 8.5 mm.; lat. 8 mm.; body-whorl 6.5 mm.; aperture 4.5 mm.; defl. 

 70 degrees. 



Some of the specimens retain their mottled coloration. The sculj^ture varies 

 much in this variety, the number of spiral ridges varying; and the ridges sometimes 

 being nodose and sometimes smooth. 



Sjiecimens pronounced variety of M. optahiVxM by Dr. Dall. 



Common in lower and rare in upper San Pedro series of San Pedro. The 

 specimen figured is the type, which is from the lower San Pedro series at San Pedro, 

 and is now in the United States National Museum. 



Fleistocene. — San Pedro (Arnold). 



387. Margarita optabilis Carpenter, var. nodosa, var. nov. 



Plate V, Fig. 13. 



Gibbula optabilis Cpr., Brit. Assn. Rept., 1863, p. 653. 



Shell small, distinctly conical, thin; whorls five, flat, and ornamented by two prominent 

 slightly nodose spiral ridges, each about one-fourth width of whorl from margin; between these two 



