THE FORAM1NIFERA 



93 



and it is important to notice this point, the forms with the largest 

 megalospheres are those which assume the biloculine condition 

 directly ; those with the smaller megalospheres repeating the 

 triloculine or the quinqueloculine arrangement. 



Family Hauerinidae. The biformed genera brought together 

 in this family are said to be characterised by the cornuspira-like 

 or milioline (tri- or quinque-loculine) arrangement of the chambers 

 in the early stages of growth. In some cases, however, as in 

 Articulina conico-articulata, Batsch, two forms of a species occur, one 

 beginning in a large globular chamber with 

 a short spiral passage leading to the later 

 chambers, which are disposed in rectilinear 

 series (Fig. 28, a), the other with a group 

 of milioline chambers at the beginning 

 (Fig. 28, b). It appears probable that 

 these represent the two forms of the 

 species, comparable with those found else- 

 where. 



Family Peneroplididae. Four genera 

 are here included Peneroplis, Orbiculina, 

 Orbitolites, and the fossil Meandropsina. As 

 Carpenter pointed out, there is in this sub- 

 family a well-marked series of forms with 

 varying degrees of complexity of structure. 

 Moreover, the contrast in the arrangement 



< ,i 111 xi_ r r 



of the early chambers in the two forms of 



the species (that of the microspheric forms 



is here, I believe, described for the first time) 



appears to offer an instructive parallel to that met with in the 



Miliolinidae and elsewhere. Hence the group will be rather fully 



described. 



Peneroplis is represented by a single species (P. pertusus, 

 Forsk.) presenting, within certain limits, a remarkable range of 

 variation. 1 In all cases the chambers are simple. During the 

 earlier stages of growth they are disposed on a planospiral plan, 

 and this may be followed until the test is complete, but more 

 usually the terminal chambers are disposed in a rectilinear series. 

 The width of the later chambers varies very much, as seen in the 

 " crozier-shaped " and broad tests represented in Fig. 29. 



Another varying feature is the " equitant " character of the 

 chambers, as the result of which the earlier convolutions of the 

 spiral part of the test are overlapped and hidden in varying 

 degrees by the alar prolongations of the chambers which succeed 

 them. The first few chambers communicate by single apertures, 

 but the apertures soon become compound, consisting of a single or 

 1 Cp. for the superficial characters of the tests, Dreyer (13). 



Flo. 28. 



Articulina conico-articulata, 

 Batsch. x about 55. a, from 

 pt. ii.). 6, from 



