ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 133 



Di*;tini;iiishaljlc' by smull size, caiicelhited surface, and luiuile in left valve. 

 Specimens identified by Dr. Dall. 



Conimon in the lower San Pedro series of Deadraan Island and San Pedro; 

 and in the upper San Pedro series of San Pedro, Los Cerritos, Crawfish George's, 

 Deudman Island, and Long Beach. Found also in the Pliocene of Pacific Beach, and 

 the Pleistocene of Twenty-sixth Street and Pacific Beach, San Diego. 



Living. — Monterey to San Diego (Cooper). 



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

 (Arnold). 



Pliocene. — San Diego (Arnold). 



62. Lucina tenuisculpta Carpenter. 



Liicina lc7iuiscnlpla Cpr., Brit. Assn. Rept., 1863, p. 642. Cooper, 7th Ann. Rept. Cal. .St. Min., 

 lcS8S, 1). 247. 



Shell small, orbicular, deeply convex, thin; umhones prominent, central ; surface sculptured 

 by numerous fine, concentric lines and radiating striae; lunule prominent, the greater part being in 

 the right valve; cardinal teeth small, laterals prominent ; anterior muscle-impressions not as elongated 

 as in L. aaitilineala and others. 



Dimensions. — Long, g mm.; alt. 8.8 mm.; diam. 6.4 mm. 



Distinguishable by small size, sculptured surface, and great convexity. This 

 species resembles Diplodonta orhella very closely in .«hape and size, but may be 

 distinguished by the lack of prominent cardinal teeth, by its lateral teeth, and by the 

 radiating striiie. Specimens identified by Dr. Dall. 



Rare in the upper San Pedro series of San Pedro. Found also in the Pleis- 

 tocene of Spanish Bight, San Diego. 



Living. — Straits of Fuca to Catalina Island; Mazatlan (Cooper). 



Pleidocene. — San Pedro; San Diego (Arnold). 



Pliocene. — San Diego well (Dall). 



Family XXIL DIPLODONTID.E. 



Genu.s Diplodonta Hroan. 



Section Diplodonid s. .«. 



Shell rotund, equilateral, externally concentrically striated or smooth, with inconspicuous 

 epidermis; two cardinal teeth in each valve, of which the right posterior and the left anterior are 

 distally sulcate or bifid: no lateral teetli; the hinge-plate when developed is usually excavated distallyj 

 there is no circumscribed lunule or escutcheon; the adductor scars are subequal, continuous with the 

 pallial line, and close to the hinge-plate; the margin is entire, the pallial line simple, and pallial area 

 often radiately striate. 



Type, Dij)lodonia lapinus Brocclii. 



