THE FAMILY NUMMULINID^ 237 



Genus Polysfomella, Lamarck. 



Supplemental skeleton, septal bridges, and canal 

 system more or less fully developed ; canals opening 

 externally at the umbilicus, and by a single or 

 double row of pores along the sutures. Aperture a 

 V-shaped line of perforations at the base of the 

 septal face. Middle Jurassic to Becent. 



Example. — P. viaceJln, Fichtel and Moll sp, 

 (Nautilus), 'Test. Microgr.' 1798, p. 66, pL x. 

 figs. e-(j. 



The chief features of this species are its com- 

 pressed form and acute periphery. The points round 

 the shell margin are often produced to a considerable 

 extent. P. macella appears to be a modification of 

 the more inflated type P. crispa. 



It is commonest in shallow water, and is found 

 in all parts of the world excepting the extreme 

 northern and southern portions. Jurassic to Becent. 

 (Plate 13, fig. D.) 



The sub-genus Faujasina, D'Orbigny, includes 

 certain forms which, although exhibiting the general 

 characters of Pol/jstouidhj, are plano-convex in 

 shape, the entire spiral portion being visible only on 

 the flat face, and the last whorl on the convex side. 

 It is isomorphous with Truucatuliiia lohatula. 



The type form F. cariuata (D'Orbigny, ' Foram. 

 Foss. Vienne,' 1846, p. 194, pi. xxi. figs. 29-81) was 

 first obtained from the Chalk of Maestricht. It also 

 occurs in various Tertiary deposits. (Plate 13^ 

 figs. E, e.) Upper Glial],- to Pliocene. 



