no. 1826. MOLLUSKS OF THE GENUS BITTIUM—BARTSCH. 



399 



in our collection average a little larger than the recent shells and have 

 the base a little more strongly sculptured. Equivalents of these, 

 however, occur among the host of recent shells examined. 



Specimens examined. 



Catalogue 

 No. 



i 14849 



32223 



56003 



160893 



195157 



160080 



73724 



55995 



32210 



46929 



195158 



194388 



32220a 



55612 



109364c 



105569 



22819 

 7154a 



Locality. 



San Diego, California. 

 Monterey, California . 

 ....do 



.do. 



San Pedro Bay, California 



San Diego Bay, California (in mud on flats at low tide). 

 San Diego, California (in mud adhering to sponges)... 



San Diego, California 



,do. 



San Diego, California (described and figured). 



San Diego, California 



...do 



.do. 

 .do. 



.Mo. 



San Ignacio Lagoon, Lower California (mud flats, between 

 tides) 



Santa Barbara, California (Lower Pleistocene). 

 ....do 



Number of 

 specimens. 



i Type. 



BITTIUM (SEMIBITTIUM) NICHOLSI, new species. 



Plate 57, fig. 1. 



Shell moderately large, broadly conic, light brown. Early nuclear 

 whorls decollated, the last one smooth. Post-nuclear whorls strongly 

 shouldered at the summit, well rounded, ornamented on the early 

 turns by four spiral cords. Beginning with the third whorl, a fifth 

 cord makes its appearance, halfway between the one at the summit 

 and its neighbor, which rapidly develops until it equals the others in 

 strength. In addition to the spiral sculpture, the whorls are marked 

 by numerous, strongly retractive, axial ribs, of which 14 occur upon 

 all the turns. The spiral cords pass over the axial ribs as bands and 

 render the junctions of the cords and ribs tuberculate, the tubercles 

 being elongate with their long axes coinciding with the spiral sculp- 

 ture. The spaces inclosed between the spiral cords and axial ribs 

 are very elongate, rectangular pits, with their long axes parallel with 

 the spiral sculpture. Sutures strongly channeled. Periphery of the 

 last whorl marked by a broad channel which shows several slender, 

 spiral threads and the feeble continuations of the axial ribs. Base 

 somewhat concave in the middle, marked by nine spiral cords, of 

 which the two immediately below the periphery are equal and much 

 stronger than the rest, which are also equal and equally spaced. 

 Entire surface of spire and base crossed by numerous, slender lines 

 of growth. Aperture oval, channeled anteriorly; posterior angle 

 acute; outer lip thin, showing the external sculpture within and some- 



