FORAMINIFERA. 113 



our recent seas. Of the remaining types of the Lituolida, 

 the genus Saecammina merits special mention as being the 

 only Foraminifer which in Britain actually forms a limestone. 

 It consists of free spherical, pyriform, or fusiform chambers 

 (fig. 21), sometimes separate, sometimes united end to end 

 in twos or threes, with thick, internally labyrinthic walls. 

 The central chamber communicates with the exterior by a 

 single aperture, and the average length of the chambers 

 of the British Carboniferous species ($accammina Carteri, 

 Brady) is as much as l-8th inch. It forms beds of lime- 

 stone in the Carboniferous of the South of Scotland and 

 North of England ; but the genus is not known to occur 

 again till we meet it in the Post-Pliocene, and, in a living 

 state, in the North Sea. The genus has also been found 

 recently in the Lower Silurian rocks of Scotland. In the 

 Nodosinella of the Carboniferous we have another curious 

 type, closely resembling the well-known Nodosaria in form, 

 but having a sub-arenaceous, imperforate test. A still more 

 singular form is the Staclieia of the Carboniferous, in which 

 the test is also sub-arenaceous and imperforate, but grows 

 parasitically upon foreign bodies, in the shape of a crust 

 composed of " an acervuline mass of chamberlets " (Brady). 

 Lastly, we must place here the extraordinary and colossal 

 extinct forms which have been described under the names of 

 Parkeria l (Carpenter) and Loftmia (Brady). Both of these 

 are arenaceous in texture, and both have a very complex 

 and truly " labyrinthic " internal structure. Parkeria occurs 

 in the Upper Greensand of Britain, in the form of spheres, 

 which are sometimes over an inch in diameter ; while Lof- 

 tusia is found in the Eocene Tertiary of Persia, and has a 

 fusiform shell which may attain a length of between two and 

 nearly three inches. 



PERFORATE FORAMINIFERA. The forms included under 

 this head have a calcareous shell more or less freely perfor- 

 ated by pseudopodial apertures, and they form a great series, 

 of which only a few of the most important forms can be 

 noticed here. 



1 According to Mr Carter, ParJceria is a Hydrozoon allied to the recent 

 Hydractinia. 



VOL. I. H 



