FISSURELLIDAE 97 



I to 2 inches in maximum diameter. Similar to D. cayenensis but differs 

 in that: (i) every second radial rib is larger; (2) concentric threads are more 

 distinct and, by crossing the ribs, form little squares; (3) radial ribs often 

 have nodules or scales. Color usually white, cream or gray, sometimes with 

 obscure radial bands. Intertidal. Common in the West Indies. 



Diodora minuta Lamarck Dwarf Keyhole Limpet 



Southeast Florida and the West Indies. 



/4 inch in maximum diameter, rather thin, depressed. Apex at anterior 

 third of shell. Base elliptical, raised slightly at the center, so that the shell 

 rests on its ends. Short front slope slightly concave, back slope convex. Ori- 

 fice narrow and trilobated. Exterior shiny, with numerous, finely beaded 

 radial ribs. Color white, with many of the ribs entirely or partly blackened. 

 Margin very finely crenulate. Internal callus around hole frequently bounded 

 by a black line. Not very common. Dredged 6 to 72 fathoms, but has been 

 picked up on beaches. Do not confuse with D. dysoni which is more likely 

 to be encountered, especially at Sanibel Island. 



Diodora dysoni Reeve Dyson's Keyhole Limpet 



Plate lyn 

 Florida, the Bahamas and West Indies to Brazil. 



H to % inch in maximum diameter, depressed and with straight sides. 

 Base ovate. Apex slightly in front of the middle and characterized by a blunt 

 knob situated behind the posterior wall of the small, almost triangular orifice. 

 Sculpture of 18 strong ribs with three smaller ones between, and with nu- 

 merous concentric lamellae. Color milky-white or cream with 8 solid, broken 

 or dotted black rays. Margin sharply crenulated with the denticles arranged 

 in groups of four. Distinguished from cayenensis by the shape of the orifice. 

 Moderately common, sometimes washed ashore. 



Diodora aspera Eschscholtz Rough Keyhole Limpet 



Plate 1 8b 

 Cook's Inlet, Alaska, to Magdalena Bay, Mexico. 



I % to 2 ^ inches in maximum diameter, slightly less than Vs as high. The 

 roundish to slightly oval, flat-sided apical hole is Mi the length of the shell 

 and about Vs back from the narrow, anterior end of the shell. Sculpture of 

 coarse radial and weaker concentric threads. Color externally is grayish 

 white with about 12 to 18 irregularly sized, purplish blue, radial color bands. 

 Commonly found clinging to rocks at low tide. In the south, dredged no 

 deeper than 20 fathoms, and often found on the stems of kelp. 



