412 



DK. A, H. COOKE ON THE 



Group 5. Subgenus Imbricaria Scluimaclier. 



Rhachidian witli 2 large and 2-3 small cusps : laterals with 

 one or more cusps considerably developed, remainder either 

 numerous or few and degraded. 



Text-figure 7. 



Lateral and rhacliidian tooth of Imbricaria marmorata Swains. 



1. /. marmorata Swains. Upoln. Rhachidian 5-cusped, all 

 sharp and projecting beyond the upper margin, the central small, 

 flanked on each side by a very large cusp, outside these one small 

 cusp, with sometimes a trace of a second ; all these are set upon 

 a thick plate, the base of which is somewhat angled in the middle ; 

 laterals with 12-14 cusps, the third from the inside much the 

 largest, inside this are 1 or 2 small denticles, all these incline 

 slightly inwards ; outside the big cusps are 9-11 vipright, sharp, 

 narrow denticles, diminishing to mere points which continue 

 to the end of the framework ; in the central portion of the 

 lower side of the framework is a roughly triangular " false keel" ; 

 the framework itself narrows towards both ends, becoming 

 almost pointed on the inner side. 



Text-fio'ure 8. 



Lateral and rhachidian tooth of Imbricaria ossea Pease. 



Text-figure 9. 



cr^r:^ 



Lateral and rhachidian tooth of Imbricaria olivceformis Sowb. 



2. /. ossea Pease. Samoa. Rhachidian with a roughly tri- 

 angular framework, nearly all of which is occupied by 2 long 

 prominent sharp cusps, whose roots are cai-ried through to the 

 base, these are flanked on each side by 2-3 wrinkles rather than 

 cusps, their points not projecting above the slope of the upper 

 margin : laterals with the second cusp enormously developed, 



