MAZATLAN BIVALVE8 103 



latter. L. caelata is larger, with tlie rugose markings more 

 coarsely grained ; ligament concealed. L. orbella is of the 

 same size and shape, but rubbed smooth, and with the ligament 

 prominent. D. undata is closely related, but differs in having 

 an anterior lateral tooth in each valve, as well as in outline. 

 Hob. According to Philippi, loc. cit., this species and Tellina 

 pisiformis are found both at Mazatlan and in the W. Indies. 

 St. Thomas', Merle. Mazatlan ; very rare, nestling in bur- 

 rows ; L'pool Col. (D. orbella) San Diego, Lieut. Green. 

 Sta. Barbara, Col. Jewett. (D. semireticulata) Cuba, Sagra: 

 Brazils ; Bio de Janeiro ; Patagonia ; D' Orbigny. 

 Tablet 479 contains 4 pairs and 2 valves, young and flatten- 

 ed. 480, 2 pairs adult. 



^|. 150. (b .) DlPLODONTA ? SEMIASPERA, 'Car. DISCREPANS. 



D. ? semiaspera t. tenui, leviori, impressione postica sub - 

 rotundatd; dentibus elongatis, ligamento omnino externd. 



Tablet 481 contains a solitary specimen, which, had the other 

 shells been at all constant in their characters, would have been 

 considered a distinct species. As it is, it must await the 

 examination of further specimens, especially as L. orbella, 

 Gould, appears intermediate between this and the typical form. 

 Long. '29, lat. '31, alt. '021. 

 Hob. Mazatlan ; 1 sp. in burrow from Chama ; Upool Col. 



151. DlPLODONTA OBLIQUA, Phil. 



Zeit.f. Mai. 1846, p. 20, no. 6. 



This species is said by Philippi to differ from D. trigonula 

 in being more oblique, with the umbos not so sharp, and the 

 dorsal margin not so straight. The umbo is placed at one third 

 of the entire breadth. Long. "12, lat. *17, alt. *06. 

 Hob. Mazatlan, Philippi. Do. ; one worn valve from the 



Chama washings ; Lpool Col. 



Tablet 482 contains the valve. 



GENUS 



A group of very nearly allied species, described by Beeve 

 and D'Orbigny as Lucinse, viz. Lucina Candeana, (Cuba,) L. 

 cornea, (coarse sand, 10-13 fm., Gulf of Nicoyia, Cuming,) L, 



