MAZATLAN BIVALVES 103 
latter. L. celata is larger, with the 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. 
Hab.—According to Philippi, loc. cit., this species and Tellina 
pisiformis are found both at Mazatlan and in the W. Indies.— 
St. Thomas’, Merk.—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; Rio de Janeiro; Patagonia; D’Orbigny. 
Tablet 479 contains 4 pairs and 2 valves, young and flatten- 
ed.—480, 2 pairs adult. 
150. (b.) DIpLoponTA ? SEMIASPERA, va7’. DISCREPANS. 
D. ?semiaspera t. tenui, leviori, impressione postica sub- 
rotundata; dentibus elongatis, ligamento omnino externa. 
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. 
Hab.—Mazatlan ; 1 sp. in burrow from Chama; L’pool Col. 
151. Diptoponta optieua, Phil. 
Zeit. f. Mal. 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. 
Hab—Mazatlan, Philippi.—Do.; one worn valve from the 
Chama washings ; L’pool Col. 
Tablet 482 contains the valve. 
GENUS 
A group of very nearly allied species, described by Reeve 
and D’Orbigny as Lucinz, viz. Lucina Candeana, (Cuba,) L. 
cornea, (coarse sand, 10-13 fm., Gulf of Nicoyia, Cuming,) L. 
