i;vl CALIFOUNIA ACADEMY OK SCIENCES. 



63. Diplodonta orbella d'ould. 



ri.ATK XVIII, ri(!S. 8 ANI> 8h. 



Liuina orbeHa Gi.u. , Proc. Host. Soc. Nat. lli.st., Vol. lY, 1S51, p. yo; Bost. Jour. N.il. Hist., Vol. 



VI, 1853, p. 395, IM. XV. lin. 3; Cal. i"v Mex. SIkIIs, ]>. 22, PI. XV, fig. 3. 

 Diplodonta orbella Gld., Goulu <Sc CarI'ENTER, Proc. Zool. Soc, 1856, pp. 202, 218. =^(Mysia) 



Sphairella lumida CoN. (Jide Cpr., Brit. Assn. Rept., 1863, p. 643). Cooi'ER, 71I) Ann. 



Rcpt. Cal. St. Min., 1888. |i. 23S. Ki:ei», West Coast Shells, p. 179, 1892. Williamson, 



Proc. U. S. Nat. Mus., Vol. XV, 1892, j). 190. Dall, Trans. Wagner Inst. Sci., Vol. 



Ill, Part 5, 1900, p. 1 189. 



Shell small, siibglobose, thin; beaks nearly median, not prominent; surface sculptured with 

 fine incremental lines, whicli at some parts arc more consjiicuous than at others and render the surface 

 somewhat irregular; no distinct hmulc; ligament prominent; two cardinal teeth in riglit valve, of 

 which the anterior is smallest, and the posterior bifid; and two in the left valve, of which tin- .interior 

 is bifid, and the posterior very obliijue; no lateral teeth; muscle-impressions large, faint. 



Dimensions. — Long. 11. 9 mm.; alt. 11.9 mm.; diam. 9 mm. 



Resembles Lncina tenuisculpin, but may be tlisLinfiiiishetl by lack of nidiiUiiig 

 .striii', ami by tbc prominent cardinal teeth and lack of lateral teeth. S])ecimens 

 identified by Dr. Dall. 



Rare in the lower San Pedro scries at Deadiiian T.'^lniid; and llic ii]iiicr San 

 I'edro series of San Pedro and Crawfish Geor>;;e's. Poiiiul al.^o in the I'leiHlocuiie of 

 Twenty-sixth Street, San Diego. The specimen figured is from the lower San Pedro 

 series of Deadman Island, and is now in the collection of Delos Arnold. 



Living. — Straits of Fuca to San Diego (Cooi^er). 



Pleistocene. — San Pedro to ,San Diego (Cooper): San Pedro; San Diego 

 (Arnold). 



Pliocene. — San Diego well (Dall). 



64. Diplodonta serricata Reeve. 



Platk XVI II, Fn;s. 5 and Hit. 



Diplodonta serricata RvE., Cpr., Brit. Assn. Rept., 1856, p. 248. 



Shell small, orbicular, only slightly convex, thin; umbones central, not prominent ; surface 

 sculptured with numerous fine, incremental lines, which are regular in prominence; lunnle ncii distinct; 

 hinge prominent; teeth and interior as in D. orbella. 



Dimensiotis. — Long. 13.8 mm.; alt. 14 mm.; diam. 7 mm. 



Distinguisihable from T). orlidla by its much less convexity and morn regular 

 concentric lines. Specimens identified by J)r. Dall. 



Not uncommon in the upper San Pedro series of San Pedro. This species is 

 very common in the Pleistocene dcjiosits at Twenty -sixth Street, San Diego. The 

 specimen figured is from this horizon, and is now in (he collection of Delos Arnold. 



Living. — Mazatlan (Carpenter). 



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



