of the Order Docoglossa. 289 



Family Patellidae, H. & A. Adams. 



Animal without a cervical gill or muzzle-frill. Rliacliidian 

 tooth rarely present ; uncini three in number, A more or less 

 complete cordon of branchise between the mantle-edge and foot. 



A. Branchial cordon complete. 

 a. Provided with a rliacliidian tooth. Aticistromesus. 



1. Ancistromesus, Dall, n. g. Two inner laterals on each side, 

 anterior to the third, which is larger and denticulate ; 

 branchial lamellaj produced, arborescent ; sides of foot 

 smooth. 

 Formula, ! .. 



' 3(1—2.2—1)3 



Type Ancistromesus mexicanus^ Dall ex Brod. & Sby. 

 (as Patella) Zool. Journ. iv. p. 369 ; Rve. Conch. Icon. 

 1855, Patella^ pi. 1. no. 1. 



h. Without a rliacliidian tooth. Patella. 



1. Patella, Linn. 1757. Lateral teeth and foot essentially as 



in the last ; branchial lamellge linguiform, short, sub- 

 equal all around. 



Formula, " 



' 3(1-2.2—1)3 



Type Patella vulgata, Linn. Syst. Nat. ed. 12. 1767, 

 p. 1258. no. 758. 



2. Patinellaj Dall, n. subg. First inner lateral on each side 



anterior to the other two ; second laterals largest, den- 

 ticulate ; foot with a scalloped frill, inteiTupted only in 

 front ; branchiae as in Patella, 



Formula, 



5 3 (2—1 . 1—2) 3 



Type Patinella magellanica, Gmel. (as Patella) Syst. Nat. 

 1792, i. p. 3703. no. 52. 

 3. Nacella, Schum. 1817. Shell thin, pellucid, apex anterior; 

 foot frilled, as in Patinella ; teeth bidentate, arranged 

 as in the last ; branchial lamellge very small in front, 

 but not interrupted. 



Formula, ^ri — r- 1 — ^o • 



Type Nacella mytilina, Gmel. Syst. Nat. 1792, vol. i. 

 p. 3698. no. 28 (as Patella) = Nacella niT/tiloides, Schum. 

 1817, and Patella cymhularia, Lam. 1819. 



B. Branchial cordon interrupted in front. Ilelcion. 



1. Helcion, Montf. 1810. Shell solid, capuloid, with pecti- 

 nated ribs : teeth ? 



