100 THE FOEAMINIFEEA 



Litmis — arietinus), ' Conch. Seesandes,' 1791, pi. vi. 

 fig. 15, c (type). 



This is a common form in the sand from the 

 shores of tlie Levant, and can often be obtained from 

 sponges. This and other forms of the genus are so 

 nearly related that they are by some authors grouped 

 as a species under the collective type-name P. 

 pertiisus. The genus is commonly found at depths 

 of less than 30 fathoms. Beceiif. (PL 4, figs. B, b.) 



P. planatus, Fichtel and Moll sp. {Nautilus 

 jjlanatus), ' Test. Micr.' 1798, p. 91, pi. xvi. fig. 1, 

 d, e, f. 



A broad complanate form with a striated surface. 

 The apertures are a single row of pores on the septal 

 face. Beceiif. (Plate 4, fig. C.) 



The. sub-generic types which call for special 

 notice are Arcliiacina, Munier Chalmas, in which 

 the test is of the P. 2)lanatus type, but the later 

 chambers tend to a cyclical arrangement ; and Mona- 

 l/jsldiu))i, Chapman, which includes the delicate- 

 shelled forms, such as those of the P. lituus type, and 

 the recent form MonaJ/jsidiujit SoIIa.'ii. (Plate 4, 

 fig. D.) 



Genus Orhiculiiui, Lamarck. 



Chambers subdivided by transverse secondary 

 septa ; early segments embracing ; arrangement 

 either piano-spiral throughout or partly cyclical ; 

 contour nautiloid, auricular, crozier-shaped or com- 

 planate. 



Example. — 0. adiinca, Fichtel and Moll sp. 



