408 DR. A, H. COOKE ON THE 



In all the above species the characteristic oi-ange colour of 

 the rhachiclian is distributed all over the framework. 



Section (b). Fapalaria Dall. — Rhachidian with 7-9 cusps ; cusps 

 short, triangular, the external set at an angle to those in the 

 centre. 



Text-figure 2. 



Lateral ami rhacliidian tooth of Mitra [Papalaria) papalis L. 



1. M. episcopalis L. Funafuti. Rhachidian 8-9-cusped, cusps 

 stout and bi'oad, set on an arching curve of the upper margin, 

 deeply rooted, base nearly straight : laterals with 20-22 cusps, 

 gradually diminishing to mere serrations at the end, inside 11 

 deeply rooted, the 3 innermost inclining inwards. 



In Mil immature specimen from S. Pacific (Cambridge) there 

 are only 5 cusps on the rhachidian, the central much the thickest 

 and longest. Troschel's figure is very poor. 



2. M. papalis L. S. Pacific. Rhachidian 7-cu§ped, the external 

 2 being obscui'e and withdrawn ; interior 5 nearly equal, central 

 slightly the largest, all set on a curved thickening of the 

 upper half of the framewoi'k, base slightly curved : laterals with 

 28-30 cusps, the interior 10-11 the largest, then diminishing to 

 mere serrations, which continue to the end. 



In both these species the 4 central cusps seem to be mounted 

 on a superposed plate, which is coloured deep orange, the rest of 

 the framework is colourless or very light yellow. 



Section (c) of M. ferruginea. — Rhachidian cusps of equal size, 

 narrow, none projecting at the sides or withdrawn behind the 

 others. 



Text-fiaure 3. 



^""^^ 



Lateral and rliacliidian tooth oi Miti-a ferruginea Lam. 



M. ferruginea Lam. Samoa. Rhachidian 6-cusped, cusps 

 rather thick and stumpy, mass of the tooth rather deep, the 1st 

 and 6tli cusps descend perpendictilarly at the sides, and there are 

 no obscure side cusps or pieces ; base very slightly arched : 

 laterals 15-17, crowded together, the 5 inside miicli the largest ; 

 about half are deeply rooted, the rest diminish into serrations 

 which continue to the end. 



