158 MAZATLAN BIVALVES 
but I disentombed the remaining valves, carefully collected 
the ditt from them, and examined their surfaces. I found 2 
perfect specimens of Pl. pernoides, and many of Lith. aristatus, 
as well as some red coral on the valves ; and among the dirt 2 
(well known African) species of Cardita, 2 of Area, 3 of Odos- 
tomia, a Chemnitzia, Fissurella, Margarita, Purpura and some 
fragments, none of them occurring on the Mazatlan coast, as 
well as Kellia suborbicularis, which is supposed to be common 
to both seas. The locality is further confirmed by the constant 
trade from Bristol to the Senegambia coast, while there was 
none (at that time) to West America. Of the specimens in 
the British Mus., one is from Anamaboa, an island in the 
W. African seas; it contains Lith. aristatus, Vermetus glom- 
eratus, and two young specimens of Placunanomia which 
agree with Pl. pernoides in all respects except that the colour 
is lighter. This is probably from youth and want of lhght, as 
I discovered them at the bottom of a Lithophagus burrow, 
tightly wedged. The other specimen from an unknown locality, 
(2? Australia, Gray) appears to be from the same seas, from its 
having the same Lith. aristatus, the same Vermetus, 2 attached 
valves of the same Placunanomia, as well as a young Hipponyx 
(not W. Coast Am.), Saxicava ? arctica, and a dead Lucina too 
nmperfect for identification. 
The Mazatlan shells appear when young to be destitute of 
denticles. Though normally very distinct from O. Virginica, 
yet they sometimes approach it in form, developing a very 
long and waved ligament area, which is then somewhat hol- 
lowed out inside, though never so much as in O. Virginica. 
The smallest valve identified measures ‘18: the largest, (which 
being from an unknown locality, though probably from Mazat- 
lan, I have not ventured to include in this collection,) is of 
regular growth, adherent all over to avery flat surface, and 
measures long. 9°25, lat. 6°3, alt. 2°07. My African valve 
which is of more normal shape, measures long. 8°3, lat. 4°2. A 
very broad specimen measures long. 4°2, lat. 4°3. A curiously 
distorted one measures long 6°5, lat. 2°8; of the length almost 
(when perfect, quite) one half consists of hinge area, in lami- 
nated chambers ! 
Hfah.—Panama ; attached to ledges of rock by the greater part 
of the lower valve, near half tide level, not common; C. B. 
Adams.— West Coast America, Hinds.—Guacomayo ; on 
rocks at low water; Cuming—Mazatlan ; very rare; D’poo! 
Y Havre Coll.—W. coast Africa; v. supra. 
