THE FAMILY MILIOLID.E 93 



as in a Spirolocidina, or two of the same intersecting 

 in different planes. 



In Signioilina the chambers are arranged alter- 

 nately at both poles of the megasphere, with a 

 centrifugal or rotary twist of growth, so that a 

 transverse section of the test shows the chambers 

 grouped in sigmoidal fashion. Usually there is 

 an extensive deposit of shell substance round each 

 chamber-wall. (See Plate 3, figs. K, /.■.) 



Suh-family 3. Haueeinin-E. 



The test in this group is dimorphous — that is, 

 exhibiting two different plans of growth at different 

 stages of the shell-development. The chambers are 

 partly milioline and partly spiral or rectilinear. 



Genus Articulina, D'Oebigny. 



The shell commences with a milioline series of 

 chambers, afterwards followed by a straight series. 

 Lower Eocene to Becent. 



Example. — A. Sagra, D'Orbigny, De la Sagra's 

 ' Hist. Phj^siq.' &c., Cuba, 1839, ' Foraminiferes,' 

 p. 183, pi. IX. ligs. 23-26. 



One of the interesting ornate forms, found chiefly 

 in the vicinity of coral reefs, as in the West Indies 

 and at the Fiji Islands. The early milioline 

 chambers are clearly seen in this species ; the aper- 

 ture is a lengthened curved slit. Becent. (Plate 3, 



