308 MAZATLAN UNIVALVES 
Tablet 1497 contains a sp. ‘08 across, on Pisania insignis, 
containing’ 4 regular sinistral whirls, like Planorbis spirorbis. 
It is smooth, and may be the same species as the above, the 
diameter being about the same ; but the colour is much deeper. 
Hab.—Mazatlan ; extremely rare; L’pool Col. 
308. ?? Brvonta ————-, sp. ind. (b.) 
Tablet 1498 contains a scarcely spiral white shell wandering 
hke an Annelid over a Byssoarca solida. The texture however 
appears Molluscan. It has two very stout rounded keels on 
the back. The same sp. displays the attached valve of Hip- 
ponyx serratus. 
Hab—Mazatlan ; extremely rare; L’pool Col. 
Gents PETALOCONCHUS, Lea. 
. 
‘ 
Animal ignotun. 
Testa extus “‘ Bivonie”’ simillina ; intus, transversim raris- 
simeé septata ; anfractibus mediantis, laminis elongatis spiralibus 
varie dispositis, cameram sepé pene secantibus ; plerumque 
duabus majoribus, tertid, quasi plicd columellari, minore. 
Operculum | specierum duarum | parvum, tenuissimum, corne- 
um, leve, subplanatum, vix spirale. 
H, C. Lea, Trans. Am. Phil. Soc. 1843, vol. ix. p. 229.— Woodw, 
Man. Moll. pt. 3, p. 462.— Monogr. in Proc. Zool. Soe. 
July, 1856. 
The remarkable internal structure in many species of Ver- 
metide, appears to have been overlooked by English naturalists, 
although it was observed many years ago by Lea in a fossil 
species. Three species in my collection from different seas 
having presented clear difference of external structure, I had 
*proposed for them the name of Macrophragma, which is now 
retained for the typical, though small, Mazatlan species. Mr. 
Cuming having most obligingly allowed me to open several of 
his specimens, nine species have been found, which are des- 
eribed in the Proc. Zool. Soc. They cannot be distinguished 
externally from Bivonia, which even as species they most 
closely resemble. The shell has somewhat the same relation 
to Vermetus that Nerina has to Cerithium, 
