ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 285 



[S. D] Odostomia (Oscilla) grammatospira D. <(■ /}., sp. nov. 



I'l.ATK I, FiCS. (i AND 6(1. 



Sliell elongate-conic, subtliaphanous lo milk wliile; nuclear whorls three, one-half obliquely 

 iinnitTsed; 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 eacli 

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

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

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



Diiiiensiivis. — Long. 5.'^ mm.; diam. 2.1 mm. 



'I'lic ly[K' lias ciglit po.st-iuiclear wliorls. It was collected at Cape St. Lucas, 

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

 ImmIs of Sail Diego are referable to this species. 



Subgenu.s Ivara D. if li. (iiis,s.) 

 Odostomias characterized by the spiral striation and tabulated whorls. 



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



Pl.ATK IV, FUi. 14. 



/vara terricula CPR. (mss.), D. & B., 1901. 



Sliell 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. 



Dimensio7ts. — Long. 4 mm.; lat. i.S mm.; body-whorl 2.6 mm.; aperture 1.5 mm. 



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

 delicate spiral scnli)ture. 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 Island. One specimen, which is 

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



Living. — Mexican Coast (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. 



