of the Order Docoglossa. 289 



Family PateUidae, H. & A. Adams. 

 Animal without a cervical gill or muzzle-frill. Rliachidiau 

 tooth rarely jiresent ; uncini three in number. A more or less 

 complete cordon of branchi^ between the mantle-edge and foot. 



A. Branchial cordon complete. 

 «. Provided with a rhachidian tooth. Ancistrom.esus. 

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

 anterior to the third, which is larger and denticulate : 

 branchial lamellae produced, arborescent ; sides of foot 

 smooth. 



Formula, ^ 



' 3(1—2.2 — 1)3 



Type Ancistromesus mexi'canus, Dall ex Brod. & Sby 

 (as Patella) Zool. Joui'n. iv. p. 369 ; Eve. Conch Icon 

 1855, Patella, -pll. no. 1. 



h. Without a rhachidian tooth. Patella. 



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



m the last j branchial lamellae 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. Patinella,p^\\^ n. subg. First inner lateral on each side 



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

 ticulate ; foot with a scalloped frill, intemipted only in 

 front ; branchiae as in Patella. 



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

 . 1792, i. p. 3703. no. 52. ' ^ - 



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



toot trilled, as m Patinella ; teeth bidentate, arranged 

 as m the last ; branchial lamellse very small in front 

 but not interrupted. ' 



Formula, ^_^^^ 



" V 2 2 • 2 ■2) <* 



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

 p. 3698. no. 28 {^& Patella) = Nacella mytilo{des,^c\ium. 

 1817, and Patella cymbularia, Lam. 1819. 



B. Branchial cordon interrupted in front. Helcion. 



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

 nated ribs; teeth? ^ 



