214 MAZATLAN UNIVALVES 
This species scarcely differs from F. nigropunctata, Sow. 
except in the entire absence of black dots round the margin. 
Shell with very numerous fine ribs, with still finer ones between, 
sometimes slightly nodulous. Outline more or less oval, more 
or less conic; growth regular. Hole large, subcentral, deeply 
chiseled, oval, constricted in the middle externally, where it is 
bilobed. Colour olive green, often stained with red when 
polished. Surface frequently eroded. Interior from pale to 
dark green ; margin crenated by the ribs; callus rather thick, 
radiately corrugated, not bounded by a dark line. Muscular 
impression distinct. The young shells (which were very rare) 
are shaped like the adult, with the hole even larger in propor- 
tion. The largest sp. measures long. 2°2, lat. 1°66, alt. °8. 
An elongated sp. 3 pe ene Poo, a eecOene 
A flattened sp. a en todoeme at AG, aba 
A rounded sp. a eNO Nae OL AO ye core 
A conical sp. ts 59) .¢ L705 3; | US4a ee 7. 
The smallest sp. be 18; “i (DG meso: 
with a hole ‘13 by ‘08.—Div. 100°—120°. - 
Hat.—Panama ; in exposed situations at low water; Cuming.— 
Do.; common, on a ledge of rather smooth rocks, between 
half tide and low water mark, in a place somewhat exposed 
to the sea; C. B. Adams. Mazatlan; very common; 
TP’pool Col. 
Tablet 1024 contains 10 sp., various ages, normal state,— 
1025, 4 do., elongated form. —1026, 4 do. flattened form.— 
1027, 3 do. rounded form.—1028, 2 do. conical.—1029, 2 do. ribs 
strong.—1030, 2 do. ribs faint. 
Tablet 1031 contains 2 sp. surface cleaned, shewing red tint 
beneath.—1032, 5 sp. shewing shades of colour within.—1033, 
2 sp. diseased from worms, &c.—1034, 1 sp. hole irregular 
through accidental breakage. 
Tablet 1035 contains a remarkable monstrosity with 2 holes. 
The first is in all respects normal. The second is adjacent 
anteriorly, perfectly round, with a thick callus within, united 
to that of the normal hole posteriorly, anteriorly rather 
pointed.* 
* A similar monstrosity appears in a specimen of F. ornata in Mr. Nuttall’s 
collection. The shell is abnormally conical, with the hole nearly round instead 
of oblong, bilobed. The second hole commences 3-5ths down towards the anterior 
margin, is very minute, and finds its exit close to the other at the apex. Itis 
surrounded by a thick callus. A still more remarkable monstrosity, without a 
hole at all, exists in D’Orbigny’s Col. vy, B. M, Cat, D’ Orb, Moll, p. 51, no, 435. 
