110 



PROTOZOA. 



recent seas. It abounded in Eocene times, one of the 

 Tertiary limestones of the Paris basin being known as the 

 " Miliolite limestone," in consequence of its being largely 

 made up of the shells of a MUiola. In Peneroplis (fig. 18, 

 c) the shell is a flattened spiral, which expands very rapidly 

 in its last half turn, the mouth running along the length of 

 the base, and being constituted by numerous isolated pores. 

 It ranges from the Eocene to the present day. Much more 

 complicated types of the Miliolida are .Alveolina and Orbit- 

 olites. The former has a comparatively large fusiform shell, 



Fig. 19. Dactyloporidse. A, Dactylopora eruca (recent) magnified 30 diameters, and viewed 

 from the inner face ; B, Dactylopora annulus, from the Eocene Tertiary, magnified 40 diam- 

 eters, viewed in profile, and showing two superimposed rings ; c, The same viewed from above 

 and similarly magnified ; D, Part of the column of Dactylopora reticulata (Tertiary), viewed in 

 profile, and similarly enlarged ; E, Fragment of Muschelkalk, with tubes of Gyroporella cylin- 

 drica, of the natural size ; F, Transverse section of a tube of the same, enlarged 10 diameters ; 

 o, Vertical section of the same, enlarged 12 diameters. (Figs. A D are after Carpenter ; figs. 

 E o are after Giimbel.) 



consisting of many layers of chambers rolled up spirally 

 round an elongated axis, the last series opening by a row of 

 pores ; and it dates from the Cretaceous, and has largely 

 contributed to the formation of various of the Tertiary lime- 

 stones. The latter is coin-shaped, sometimes more than half 

 an inch in diameter, and very complex as regards the arrange- 

 ment of its chambers. The genus is especially abundant in 



