OBYPTOPLAX, 



nusCRYPTOl'LAX Ulainville, 1818. 



/'/./ UI.AINV., I>ict. dee Sci. Nat. xii, p. 124, for C. larri- 

 forniis and depressm. Chitonellus LAMARCK, An. sans Vert, vi, p. 

 .,17. lor ( '. A/n> and >/rm/iw (1819.) Ametrogephyrus MIDD., Mai. 

 Ross, i, p. 33, (1847). 



Much elongated, distinctly vermiform, the valves not nearly cover- 

 ing the entire dorsal surface, the posterior ones either separated from 

 one another or in contact merely at their tips. Insertion and sutural 

 plates very strongly drawn forward, the anterior valve having three 

 slits, the other valves none. Girdle minutely setose, generally hav- 

 ing minute sutural pore-tufts. Gills occupying the posterior third 

 of the branchial groove. 



Distribution, Philippines to Tasmania and Polynesia. 



In this genus the sutural-lamina3 of each valve are entirely 

 separated from the valve next forward, although they are deeply 

 inserted in the muscular integument of the back. The number of 

 slits is more reduced than in any other forms having insertion-plates, 

 approaching in this respect the LepidoplewridcK* 



Only four species of this genus are recognized by Haddon, in his 

 -ion of the genus in the Report on the Polyplacophora collected 

 by the Challenger Expedition. They may be recognized by these 

 marks : 



C I .am. Large or medium sized, convex above, flat below, 



the valves all in contact or nearly so, conspicuously wrinkle-sulcate 

 at the sides, with a smooth dorsal band. Pores present or absent, 

 the girdle densely spiculose, without a ventral bounding fringe. 



C. burrowi Sm. Small ; valves iv, v, vi and vii very small and 

 widely separated from one another; grooved at the sides, with 

 smooth central bands. Pores minute. 



C. oculatus Q. & G. Smaller, having the latter four valves 

 separated, longitudinally grooved at the sides, having triangular 

 smooth dorsal areas. Pores wanting. Several front valves sur- 

 rounded \\ith fringes of black and of white bristles. 



C. larvajonni< Blv. Large, cyclindrical, having the latter four 

 valves widely separated, sculptured with grooves con verging forward 

 to a dorsal sulcus, sometimes ill-defined. Minute pore-bunches 

 generally present; having a fringe of spicules bounding the ventral 

 surface. Anterior several valves eroded, not surrounded with black 

 and white fringes of spicules. 



