ARNOLD — THE PALEONTOLOGY AND STl?.VTI(>RAriIY OF SAN PEDKO. 285 



[S. D.] Odostomia (Oscilla) grammatospira D. d- /}., sp. iiov. 



PlaTK I, FifiS. 6 AND 6rt. 



Shell elongate-conic, subdiaphanous to milk white; nuclear whorls three, one-half obliquely 

 immersed; post-nuclear whorls flattened, traversed by four very strong, flattened, decidedly raised 

 spiral ridges, which are separated by furrows of about the same width; the sutures being marked 

 by a little wider groove than those between the spiral ridges; the spiral depressions are very finely 

 and closely axially ribbed; the base of the last whorl is ornamented by similar sculpture, but of a 

 weaker character, the spiral ridges diminish gradually in size and at the same time approach each 

 other more closely, vanishing altogether on the extreme base; aperture subrhombic, posterior angle 

 acute, outer lip thin, arcuate, very much produced and flaring at the junction with the pillar; colu- 

 mella stout, reflexed, provided with a prominent fold at its insertion. 



Dimensions. — Long. 5.3 mm.; diam. 2.1 mm. 



Tlie type lias eight post-nuclear whorls. It was collected at Cape Bt. Lucas, 

 Lower Califoruia. Two fossil specimens in our collection from the post-Pliocene 

 beds of San Diego are referable to this species. 



Subgenus Ivara D. X- B. (mss.) 

 Odostomias characterized by the spiral striation and tabulated whorls. 



305. Odostomia (Ivara) terricula {Carpenter) D. & B. 



Platk IV, Fiii. 14. 



Ivara ierriada CPR. (mss.), D. & B., 1901. 



Shell minute, ovate, thin; spire elevated; apex acute; whorls five, convex, shouldered above; 

 surface sculptured by fine, spiral ridges and obsolete transverse ribs, more prominent near top of 

 whorls; suture deeply impressed; body-whorl over half length of shell; shouldered above, evenly 

 convex below; aperture truncated above, evenly rounded below; outer lip thin, extending around and 

 up on columella, forming a small columellar plication. 



Dimensions. — Long. 4 mm.; lat. 1.8 mm.; body-wiiorl 2.6 mm.; aperture 1.5 mm. 



This delicate little shell is easily recognized by its shouldered whorls and 

 delicate spiral sculpture. Specimen identified by Dr. Dall; but the species omitted 

 from the text prepared by Dall and Bartsch. 



Rare in lower San Pedro series of Deadman Lsland. One specimen, which is 

 figured, and is now in the collection of Delos Arnold. 



Living. — Mexican Coa-st (Dall). 



Pleistocene. — San Pedro (Arnold). 



Superfamily T.ENIOGLOSSA. 



Family LXV. TRITONID.E. 



Genus Tritonium Link. 



Shell oblong; spire prominent; whorls with a few remote and non-continuous varices; colu- 

 mella rough or smooth; canal recurved, short or long; outer lip internally crenated or denticulated. 



Tritonium variegatus Lam. is a characteristic species. 



