72 FAMILY MILIOLIDA. 



93. Affinities. — The type which has now been described is of no common interest, as 

 displaying the first nisvs of a Rhizopod towards the production of a multilocular shell, and as 

 marking out, though in a rude and indefinite form, the principal plans which are evolved with 

 much greater completeness and regularity in the higher types. Niibccularia is obviously 

 allied to Cornuspira on the one hand, and to Vertebralina on the other ; it cannot, however, be 

 said to be truly intermediate between those genera (though some of its forms approximate to 

 each), because it difi"ers from both of them in the deficiency of the shelly wall on one side, as 

 well as in the rude and almost amorphous aspect of its free surface. 



93. Geographical Distribution. — The shells of this genus are, for the most part, inhabitants 

 of the warmer seas, being especially large and abundant in the Laminarian zone, in which 

 they sometimes attain the size of hemp-seeds, or even of split peas ; whilst, when brought up 

 from deeper water, attached to the shells of large Mollusks, they are much more minute. 

 They also occur in a detached condition, associated with other Foraminifera, in many recent 

 sea-sands from shallowish water. 



94. Geoloyical Distribution. — Nuhecularia are abundant in some of the French Tertiaries, 

 have been met with attached to GrypliacB, &c., in many Oolitic Clays, and have been recog- 

 nised in abundance (though the examples were very minute) in the Triassic Clay of 

 Chellaston. 



Genm IV. — Vertebralin.\ (Plate V, figs. 17 — 25). 



95. Histori). — The genus Verlebralina was first characterised by D'Orbigny (lxix) in 

 1826 ; the name which he has assigned to it having been apparently suggested by the resem- 

 blance presented by some of its forms (Plate V, fig. 22) to the vertebral column of a Shark. 

 On account of its spiral commencement he placed it among his nautiloid Helicnslegues, though 

 admitting that its position there is anomalous (lxiii, p. 120). Its relationship to the 

 Milioline type was first clearly indicated by Professor Williamson (ex, p. 89), who has given 

 an excellent description of its characteristic form, and has very properly reunited with 

 Vertebralina striata, the V. cassis and V. mucronala, of D'Orbigny, the diiferential characters of 

 which are too slight and inconstant for their separation. He was not aware, however, of 

 the extraordinary poh/jnorphism which this type is found to display when the comparison is 

 extended through a sufficiently wide geographical and geological range. 



96. External Characters. — The aspect of the shell in Veriehralinais generally opalescentand 

 brightly polished, and its surface is usually marked by delicate, longitudinal striations, which 

 have the strength of ribs in the thick-walled and more strongly characterised specimens, such 

 as D'Orbigny's V. mucronata (xcii, PI. vii, figs. 16 — 19), but which become obsolete, or even 

 disappear entirely, on the later portions of the more delicate and more aberrant specimens. 

 More rarely the surface is pitted. The shell is complete on both sides, and is usually a 

 symmetrically flattened tube ; it has no other attachment to the surface on which it grows, than 



