PATELLID^E. 77 



An original formula is herein used to express the arrangement of 

 teeth upon the radula, not from any preference for novelty, but 

 because the new method is believed to be more graphic. 



The gill-cordon is probably always interrupted by a narrow hiatus 

 at the front left side but practically it is considered " interrupted " 

 only when absent above the neck for a considerable distance. 



An excellent paper by R. J. Harvey Gibson on the anatomy of 

 Patella vulgata, in Trans. Roy. Soc. Edinb. xxxii, pt. 2, p. 601-638, 

 5 plates, gives the most complete account yet published of the 

 anatomy, histology and physiology of Patella. Illustrations 'of 

 the dentition of various Patellidce have been published by Dall, Bars, 

 Hogg, Hutton and others. 



Numerous classifications have been proposed for the limpets. The 

 systems of the earlier authors, as well as of H. & A. Adams, are very 

 crude, being founded upon the shell alone. J. E. Gray (Guide) 

 offered a somewhat better but still very imperfect arrangement. 

 Dr. W. H. Dall in 1871, proposed a system based mainly upon the 

 gill-cordon and dentition. This was somewhat modified by him a 

 decade later in Proc. IT. S. Nat. Mus. iv, 1881, p. 412, 413 (1882). 

 His modified arrangement is as follows : 



A. Branchial cordon complete. 



a. With rhachidian tooth; branchial lamella? arborescent, pro- 

 duced; sides of foot smooth. ANCISTROMESUS. 



Ancistromesus Dall. 3 (i 212 i) 3 . 



b. Without rhachidian tooth ; branchial lamellae short, lingui- 

 form. PATELLA. 



Patella Linne. Foot smooth ; branchial lamellae sub- 

 equal all around. 3 (i 202 i) 3 . 



Patinella Dall. Foot with scalloped frill interrupted 

 only in front ; gills as in Patella. 3 ( 2 101 2 ) 3 . 



Nacella Schum. Foot frilled ; gills very small in front ; 

 shell peculiar ; lateral teeth all bidentate. 3 ( 2 101 2 ) 3 . 



B. Branchial cordon interrupted in front. 

 a. Sides of foot smooth. HELCION. 



Helcion Montf. Third laterals posterior, bidentate. 



/ 202 N 

 3U 1J3- 



Helcioniscus Dall. First laterals anterior. 3 ( 2 101 2 ) 3 . 

 Patina Gray. Third laterals posterior, denticulate ; 

 shell peculiar. 3 (i \~) 3 ' 



*** 



Metoptoma Phillips (fossil.) 



