MAZATLAN BIVALVES 529 
[The following species are out of their order, having been 
discovered among Spondylus fragments received during the 
progress of the work. | 
[Famity PETRICOLID. | 
Genus NARANIO, Gray. 
Ann. & Mag. Nat. Hist. 1853, vol. xi. p. 38.—B. M. Cat. Ven. 
p. 215. 
Petricola sp., auct. 
Choristodon, H. & A. Ad. Gen. vol. ii. p. 441: non Jonas.* 
680.t P NaRANIO SCOBINA, %. S. 
2 N. t. transversd, quadratd, albidd : extus creberrime granu- 
_ lis in lineas diagonaliter transversis, instructis ; marginibus 
incrementi, sepe extantibus ; umbone lata; satis prominente, 
ared lunulari magna: dent. card. Wi. quarum unus prominens 
et alter inconspicuus parallelis ab umbone postice radiant ; alter 
hamatus, ab altero disjunctus marginem anteriorem continuat ; 
nympho satis elongato. 
The great peculiarity of this shell is in the separation of the 
cardinal margin. One tooth is formed by the twisting round 
of the anterior margin; the other teeth, of which one is 
nearly obsolete, radiate from the umbo towards the posterior 
end; the space between being hollowed out, and as it were 
open to the outside. Only one valve was found,t which 
measures long. ‘09, lat. °13, alt. * 03. 
Hab.—Mazatlan ; 1 valve off Spondylus ; L’pool Col. 
Tablet 2516 contains the specimen. 
[Famitry MYIDZi.] 
681. ? Mya ————-, sp. ind. 
Tablet 2517 contains a hinge fragment, with a deeply sunken 
ligament-process resembling Mya. 
Hab.—Mazatlan; extremely rare, off Spondylus ; L’pool Col. 
* The Choristodon typicum of Jonas is the West Indian analogue of Petri- 
cola robusta, Sow. Having carefully compared a specimen from the sponge of 
commerce with adolescent Petricole in the Mazatlan collection, I am unable to 
detect even a specific difference between them, The shape, minute sculpture 
of the valves, and other marked characters are identical. The Petricola is 
usually seen in its adult state, with the hinge teeth nearly obliterated. 
t No. 677 belongs to the Lepralia, 678 to the Cellepora, and 679_to the 
Tubulipora, indicated in page 6. 
{ The little valve deposited on tablet 781 (vide page 169, no, 220,) appears: 
to be a different species of the same genus. 
April, 1857. La 
