Lepidoplcuru*.] AMPHINEURA. 



of each valve, sometimes the upper part of the lateral areas is also 

 brown, and the anterior valve has very often the same colour ; the 

 girdle is dirty-white. The interior of the valves is white, the anterior 

 central part of the intermediate valves is finely striate ; there are no 

 insertion plates ; the sinus is very broad and smooth ; the sutural 

 laminse are narrow, high, triangularly rounded, and semitransparent ; 

 the valve-callus well developed. 



Measurement of a large specimen : Length, 12 mm. ; breadth, 

 6-5 mm. Divergence, 90. 



Type, from Tasmania, in the British Museum. 



Hab. Coasts of the North and South Islands, under stones between 

 tide-marks ; 25 fathoms, Hauraki Gulf. Found also in Tasmania, 

 South Australia, and Victoria. 



SUBORDER 2. MESOPLACOPHORA, Pilsbry. 

 Insertion plates well developed and slit. 



Fam. ISCHNOCHITONID^, Dall. 



All the valves with slits, and the inner layer well covered by the 

 outer. Insertion plates sharp, smooth, with eaves. Posterior valve 

 with a series of well-developed teeth. 



Subfam. 1. 1SCHNOCHITONIN.E. 



The slits of the anterior and intermediate valves do not correspond 

 with external ribs. 



Genus 1. ISCHNOCHITON, Gray, 1847. 

 Ischnochiton, Gray, P.Z.S., 1847, 26. Type : /. longicymba, Q. & G. 



Valves external, having sharp, slit, insertion plates, the teeth not 

 buttressed. Eaves solid. Girdle covered with imbricating scales, 

 either flat or convex, smooth or striated. Gills typically extending 

 the entire length of the foot, but in some species they are short in front 

 or at both ends. 



Ischnochiton is the typical or central point in development of the 

 sharp-toothed division of Chitons, around which the other genera 

 naturally group themselves. 



Distribution. World-wide. 



Subgen. 1. ISCHNOCHITON, Gray (restricted). 



Lepidopleurus (part), H. and A. Adams, and Carpenter, olim ; not Lepido- 

 pleurus, Risso. 



Valves having sharp, non-pectinated insertion plates ; mucro 

 median or anterior ; girdle covered with imbricating scales. 



