MAZATLAN BIVALVES 169 
Tablet 751 contains 4 valves, extremely young.—752, 6 sp. 
usual state.—753, 2 do. concentric furrows developed.—754, 
6 do. radiating ribs strongly developed.—755, 4 sp. finely 
grown, ribs slightly developed.—756, 3 do. concentric lines 
marked.—757, 3 do. almost smooth.—758, 2 do. waxen aspect, 
like Placunanomia claviculata. 
Tablet 759 contains 3 sp. bright yellow.—760, 2 do. greenish, 
? from Conferve.—761, 2 do. with tinge of pink. 
Tablet 762 contains 3 sp. salmon tint, radiated.—763, 1 do. 
with concentric waves.—764, 1 do. with greenish.—765, 1 do. 
grown over with Vermiliz, which indent it throughout.—766, 
1 do. square form, with Vermiliz attached: (a beautiful little 
species, often found on this and other delicate shells.)—767, 4 
lustrous valves, shewing changes in the central angle of scars. 
Tablet 768 contains 2 sp. distorted growth, inflated.—769, 3 
do. corrugated surface.—770, 3 do. transverse growth.—771, 2 
do. indented.—772, 3 do. right side cut off at various angles.— 
773, 4 do. left side do.—774, 3 do. vertex, distant from margin.— | 
775, 2 do. hole smal!l.—776, 1 do. with remarkable rows of egg 
cases. 
Tablet 777 contains 3 sp. with variously formed plugs attach- 
ed.—778, a sp. with young attached: both valves are removed, 
shewing its own plug, and another small one near without 
corresponding shell.—779, another sp. with young attached ; 
the upper valve only is removed, shewing the lower in situ.— 
780, 9 pairs and valves shewing interior. 
220. ? 
—— 
» sp. ind. 
Tablet 781 contains a minute valve, (found since the first part 
of this Catalogue was printed,) of which it is hard to tell even 
the generic place. The outside has the general appearance of 
Spheenia fragilis ; extremely thin, transparent, covered with a 
copious epidermis with rather distant concentric layers; very 
inequilateral, with an obscure angle from the very projecting 
umbos to the posterior end. Hinge with two long lamellar 
teeth, one going posteriorly from the umbo, the other parallel 
to it, nearer the anterior end. Ligament apparently external, 
very thin. Long. ‘05, lat. °027, alt. °007. 
Hab.— Mazatlan ; one fresh valve off Ostrea iridescens ; 
*pool Col. 
March 1856. q 
