CLASS GASTROPODA 
147 
spiral line above and below the periphery are a little farther apart than 
the rest. Aperture large, oval; posterior angle acute; outer lip thin, show¬ 
ing the external sculpture within; provided with five strong, spiral cords, 
the anterior one of which is a little closer to its* neighbor than the rest, 
which are equally spaced; columella moderately strong, curved, and revo¬ 
lute. Length, 8.5 ; diameter, 2.3 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 46501. Type locality, 
San Diego, California. 
Range. San Pedro, California, to Todos Santos Bay, Lower Cali¬ 
fornia. 
Turbonilla tridentata Carpenter, 1865 
Plate 56, figs. 12, 12a; Plate 54, fig. 9 
Journal de Conchyliologie , 13 (3d. series, 5) :147, 1865. 
Ch. t. (quoad genus) magna compacta, latiore; castanea, interdum 
fasciis pall dioribus; anfr. nucleosis 3 helicoideis, apice conspicuo, mar- 
ginibus spirae rectis parum superantibus; normalibus ii subplantibus, 
suturis distinctis; costis rectis acutis, interdum 19, interdum 24 tenus, haud 
attingentibus, circa peripheriam haud subito evanidis; interstitiis undates, 
eleganter spiraliter, sulcatis; sulculis circiter 8-10, costis haud superantibus ; 
apertura subquadrata; labio intus tridentato; columella tortuosa; basi 
rotundata. Long., .43; long, spir., .35; lat., .12 poll. (Carpenter.) 
Shell large, broad, chestnut-colored, obscurely banded. Nuclear whorls 
three, helicoid, about one-third immersed, scarcely extending beyond the 
margin of the spire, their axis being at a right angle to the axis of the 
later whorls. Post-nuclear whorls slightly convex, somewhat contracted 
at the periphery and slightly shouldered at the summit; traversed by 
about twenty to twenty-four, strong, well-rounded, somewhat oblique, 
axial ribs, which continue faintly over the decidedly angular periphery of 
the last whorl and the base to the umbilical region; these ribs are con¬ 
siderably enfeebled on the last whorl of old shells and frequently become 
almost obsolete on these. The exposed portion of the whorls is traversed 
by five spiral grooves, which appear most prominently in the shallow and 
broad intercostal spaces, and less so on the ribs; these deep spiral lines are 
regularly spaced, leaving a broader interval on the middle of the exposed 
portion of the whorl; the base of the last whorl is likewise ornamented 
by spiral grooves, but here they appear less developed than on the spire. 
In addition to this the entire surface of the shell is marked by numerous 
very fine, somewhat wavy, spiral and axial striae, which show most promi¬ 
nently on the last whorl and base, and give the shell a very minutely reticu- 
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