6 PECTINODONTA. 



Synopsis of genera. 



I. Radula ivlth a single lateral tooth on each side ; no uncini, 



Pectinodontin^. 



Genus PECTINODONTA Dall, 1882. 

 Animal blind ; having a cervical branchial plume but no 

 branchial cordon. 



II. Radula having three lateral teeth on each side, Acm^in;e. 



Genus ACM^A Eschscholtz, 1830. 

 Animal having a cervical branchial plume but no branchial cor- 

 don ; eyes present. 



Genus SCURRIA Gray, 1847. 

 Animal having a cervical branchial plume and a complete or 

 interrupted branchial cordon. 



Subfamily Pectinodontin^. 

 Genus PECTINODONTA Dall, 1882. 



Pectinodonta Dall, Proc. U. S. Nat. Mus. 1881, p. 409, 1882 ; 

 Blake Gastrop. p 411. 



Shell resembling Scutellina but Avith a blunt subcentral apex. 

 Soft parts resembling Acmtea except in the following details : Ani- 

 mal blind, with the front part of the head between the tentacles and 

 above the muzzle much produced upward and forward, extending 

 considerably farther forward than the end of the muzzle, which is 

 marginated with lappets at the outer corners. Jaw thin, translu- 

 cent. Gill exactly as in Acnuea; sides of foot and mantle edge 

 simple, nearly smooth. Dental formula (1.0.1.) 0; teeth large, 

 with transverse pectinated or denticulated cusps, the serrated edge of 

 which is turned toward the median line. The number of teeth is 

 the smallest in any known limpet. (Dall.) 



The dentition is figured on pi. 33, fig. 74. 



P. ARCUATA Dall. PL 33, figs. 74, 75, 76. 



Shell white, elongate-ovate, moderately elevated, with a blunt 

 polished apex, on which in young specimens, remain traces of the 

 disk-like, chalky, embryonic shell ; the slopes from the apex to the 

 ends both convexly arched; margin simple or slightly denticulated 

 by the radiating sculpture ; within polished ; scars as in Acmsea ; 



