158 MAZ.ATLAN BIVALYES 



but I disentombed the remaining valves, carefully collected 

 the dirt 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 Chemnitz ia, "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, Yermetus glom- 

 eratus, and two young specimens of Placunanomia which 

 ao-ree with PL pernoides in all respects except that the colour 

 is lighter. This is probably from youth and want of light, as 

 I discovered them at the bottom of a Lithophagus burrow, 

 tightly wedged. The other specimen from an unknown locality, 

 (? Australia, G-ray) appears to be from the same seas, from its 

 having the same Lith. aristatus, the same Yermetus, 2 attached 

 valves of the same Placunanomia, as well as a young Hipponyx 

 (not W. Coast Am.), Saxicava ? arctica, and a dead Lucina too 

 imperfect 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. Yirginica. 

 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 a very 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 ! 



Hal). Panama ; attached to ledges of rock by the greater part 

 of the lower valve, near half tide level, not common; C. JB. 

 Adams. West Coast America, Hinds. Guacomayo ; on 

 rocks at low water ; Cuming. Mazatlan ; very rare ; L'pool 

 $ Havre Coll.'W. coast Africa ; v. supra. 



