176 



SYSTEMATIC ARRANGEMENT 



edge, flat and bluntly trifid ; teeth of lateral series three, shortly 

 hooked (fig. 94). 



Fig. 94. — Teeth of Patina pellucida. 



The sides of the foot of Patina pellucida are furnished with a 

 slight lobulated fringe edging the upper margin. The edge of the 

 mantle with a series of minute tentacles, just within which are placed 

 the series of gills formed of close, large, triangular transverse leaves ; 

 the series is interrupted over the head ; the mouth edged with ex- 

 panded lips. The tentacles are far apart, with the eyes at their 

 outer base. The mantle with 50 to 65 equidistant, slender, acute, 

 tentacular filaments : floating beyond the edge between its margin 

 and the body is placed the branchial cordon of 80 to 100 subtrian- 

 gular plates, so extremely close-set as to present the appearance of 

 thread-like filaments without depth, diminishing gradually anteally 

 until they are interrupted by the head. — Clark, Moll. 258. 



4. Helcion. 



Shell half-ovate, radiately ribbed ; apex submarginal, anterior ; 

 aperture ovate ; edge crenated. Gill interrupted over the head, of 

 small and filiform strands. 



1. H. pectinatus. 



Suborder VII. Polyplacophora. 



Gills in two lamellar series, one on each side of the hinder part of 

 the body under the mantle edge. Shells 8, forming a linear imbricate 

 series on the middle of the back. Lingual membrane long, linear ; 

 central series with many teeth, middle one unlike the rest, outer 

 lateral one on each side very large, with a black opake hook ; lateral 

 teeth several, forming jointed unarmed lamellae ; one erect, hooked 

 (p. 173). 



