26 Mr. W. H. Dall on Deep-water Limpets and Chitons. 
B. With an interrupted cordon ; no lappets. 
Lottia (Gray), Cpr. 1 om: 
C. With complete cordon ; no lappets. 
Scurria, Gray (not Cpr.). EI ie 
Family Patellide. 
Without a cervical branchia, but with a more or less com- 
plete cordon; muzzle papillose, not frilled, marginated, or 
with lappets. 
A. Branchial cordon complete. 
a. With rhachidian tooth; branchial lamellz arborescent, 
produced ; sides of foot smooth. Anczstromesus. 
° 1 
A ncistromesus, Dall. 3(—2.2—1) 3° 
b. Without rhachidian tooth ; branchial lamelle short, 
linguiform. Patella. 
Patella, Linné. Foot smooth, branchial lamelle subequal all 
around. Ese 
Patinella, Dall. Foot with a scalloped frill, interrupted only 
in front; gills as in Patella. se 
Nacella, Schumacher. Foot frilled; gills very small in 
front; shell peculiar ; lateral teeth all bidentate. 
B. Branchial cordon interrupted in front. 
a. Sides of foot smooth. Helcion. 
Helcion, Montfort. Third laterals posterior, bidentate. 
Helcioniscus, Dall. First laterals anterior. ae 
Patina, Gray. Third laterals posterior, denticulate; shell 
. 0 
peculiar. 3(1—2.2—1) 3° 
& & % * % * 
Metoptoma, Phillips. Posterior edge emarginate or waved. 
Fossil in Carboniferous of Great Britain. 
January 22, 1882. 
