214 



MAZATLAK UNIVALVES 



This species scarcely differs from F. nigropnnctata, Sow, 

 except in the entire absence of clack 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 

 dart 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. 1*7, , 1'22, , "65. 



A flattened sp. 

 A rounded sp. 

 A conical sp. 

 The smallest sp. 



1'95, 

 175, 

 175, 



8, 



1'48, 

 1-49, 

 1'34, 

 56, 



62. 

 67. 

 77. 

 2, 



with a hole '13 by '08. Div. 100 120. 



Hob. 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. IB. Adams. Mazatlan ; very common ; 

 I/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. NuttalTs 

 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. It is 

 surrounded by a thick callus. A still more remarkable monstrosity, without a 

 hole at all, exists in D'Orbigny's Col. v. . M. Cat, D'Oi-b. Moll. p. 61, no. 435. 



