KEPORT ON THE POLYPLACOPHORA. 27 



Owing to the corrosion of the umbo the measurements of the length of the valves are 

 not absolutely accurate, and as most of the specimens are curled the total length of the 

 body is only approximate. 



From this table it will be seen that the ratios of the length to the breadth of the 

 valves is the same in Acanthopleura granulata, A. and B., but the valves are relatively 

 shorter in Acanthopleura sp., C. 



It appears that the valves are relatively very slightly longer in Acanthopleura 

 spiniger than in Acanthopleura granulata (A. and B.), but the ratio in Acanthopleura 

 incana is as nearly as possible the same. 



Analysis of Under Surface of Valves. 



Anterior valve. — Acanthopleura granulata, A. and B., 13 slits; teeth long, the 

 central as a rule green in colour, the lateral usually brownish ; eaves short ; colour pale 

 slate or pearly gray, dark brown jugum. Acanthopleura sp., C, 12 slits; teeth short, 

 all green in colour ; eaves long ; colour pale greenish gray, dark brown jugum but 

 smaller than in former. Acanthopleura spiniger, 10 slits; teeth long, dusky colour; 

 colour pale dusky brown. Acanthopleura incana, A., 11 slits; teeth short; eaves short; 

 colour uniform very dark brown; B. 10 slits, darker colour; C. similar, but with pale 

 teeth. 



Intermediate valves. — Acanthopleura granulata, A. and B., colour greyish ; jugum 

 dark brown ; sutural laminae pale, more or less splashed with brown ; posterior border of 

 anterior laminae deeply grooved. Acanthopleura sp., C, colour pale sea-green ; jugum 

 dark brown ; sutural laminae of uniform colour, with their posterior border very slightly 

 striated; the jugal insertion-plates are narrower than in the former. Acanthopleura 

 spiniger, colour uniform greyish brown; jugum darker brown; anterior laminae paler 

 brown ; posterior border of sutural laminae coarsely grooved. Acanthopleura incana, 

 colour uniform very dark brown to black; anterior laminae same colour; posterior border 

 of sutural laminae slightly grooved. In C. the sutural laminae become lighter anteriorly, 

 the rim being nearly white. 



Posterior valve. — Acanthopleura granulata, A. and B., 10 to 12 slits; teeth long, all 

 green, or anterior tinged with brown ; eaves short ; colour white ; jugum brown. Acantho- 

 pleura sp., C, 11 to 12 slits; teeth short, green, set more obliquely than the former, and 

 with considerable symmetry with the median line, eaves long. The eaves are so long that 

 when the valve is placed on a smooth surface and viewed on a level with the eye, the 

 teeth are entirely hidden, whereas they are seen to nearly their whole extent in the former 

 species ; colour white and pale green ; jugum small brown spot. Acanthopleura spiniger, 

 7 or 8 slits ; teeth long, greenish; eaves short ; colour, posterior border and jugum brown, 

 between them a greenish band. Acanthopleura incana, teeth entirely absent ; colour and 



