Dall.] 52 [October 19, 



Type L. gigantea (Gray) Cpr., Am. Journ. Conch., n, p. 342. 

 1866. 



C. Cordon present; complete, uninterrupted. Scurria. 



1. Scurria Gray, 1847. No muzzle lappets. Teeth as in the last. 

 Formula, 1{2 J 1 _ 2)1 - 

 Types S. scurra (Lesson) Gray, P. L. S., 1847, p. 158. S. 



mesoleuca (Mke.) Cpr., Maz. Cat, p. 208, no. 263 (as 



Acmcea). 1857. 



Family Patellidj; H. & A. Adams. 



Animal without a cervical gill or muzzle frill. Bhachidian 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 rhachidian tooth. Ancistromesus?- 



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

 anterior to the third, which is larger and denticulate. 

 Branchial lamellaB produced, arborescent. Sides of foot 

 smooth. 



F ° rmula ' 8(l-2 1 2-l)3 ' 



Type Ancistromesus mexicanus Dall ex Brod. & Sby. (as Pa- 

 tella) Zool. Journ., iv, p. 369. Rve. Conch. Ic, Patella, 

 pi. i, no. 1. 1855. 



b. Without a rhachidian tooth. Patella. 



1. Patella Lin., 1757. Lateral teeth and foot essentially as in the 

 last. Branchial lamellse linguiform, short, subequal all 

 around. 



F ° rmula ' 8(l-2°2-l)3 ' 



Type Patella vulgata Lin., Syst. Nat., Ed. 12, p. 1258, no. 

 758. 1767. 



1 From AyKiOTQov, a hook or tooth, and peoog, median or middle. 



