GENUS MILIOLA. 75 



to millet-seed borne by the minute bodies to which it is applied. The Lamarckian genus was 

 adopted by various subsequent writers ; its name being modified to 3Iilio/rt or Miliolina for 

 the purpose of including the recent forms, which diifer in no essential particular from the 

 fossil. But in M. D'Orbigny's first systematic ari'angement of the Foraminifera (lxix) he 

 broke up this genus into the genera Uniloculina, Biloculina, Triloculina, Quinquelocidina, Sjpiro- 

 loculina, Adelosina, and CriicilocuUna ; and these he associated with Sjiharoidina (of which the 

 examples he cites as typical are really allied to Glohii/erinn, having a perforated hyaline 

 shell), and Articidina (which is in reality a varietal form of Vertcbiyi/lna, ^ 90), into his Order 

 AgathistivGUES ; his definition of which might have served as the generic character of 

 Miliula, if it had been founded on a correct conception of its typical structure. To the fore- 

 going genera, D'Orbigny subsequently added Fabularia (at first wrongly placed by him else- 

 where), a type which will hereafter be shown to present a peculiar development of the Milio- 

 line (1 116). Our reasons for reuniting the first seven of the genera just enumerated, with 

 all their multitudinous species, under the single type Miliola, without attempting to establish 

 even specific differentiations, will presently become apparent. With regard to his generic 

 divisions it is not a little singular that M. D'Orbigny should have remarked as follows : — 

 " We tliink it diflicult to find genera more distinct one from another than are those of this 

 Order. They present forms so sharply defined, that there really exists no transition between 

 them; and thus any one by a few liours' study will always find himself able to distinguish 

 them " (lxxiii, p. 256). Now although a few hours' study, prosecuted after the fashion of 

 M. D'Orbigny, may lead to an acceptance of his generic and specific distinctions as valid, yet 

 in precise proportion as that study is prolonged, and is made to include a sufiiciently large 

 number of examples of this type, brought from all the seas and from all the geological deposits 

 in which it occurs, do its results pi'ove to be of quite an opposite character. For the types 

 which were represented by M. D'Orbigny as so sharply defined, are found, on careful compa- 

 rison — as has been shown by Mr. W. K. Parker (lxxv) on whose view of tliis genus my own 

 account of it is based — to graduate into one another so insensibly, that no line of demarcation, 

 either specific or generic, can be drawn between them; so that no middle course can be 

 adopted between ranking them all as varieties of one species, distinguished by the degree 

 and direction of their divergence from a central type, and multiplying almost indefinitely 

 the number of species by adopting the most trivial modifications of form or surface-marking 

 as differential characters. This truth has already been partly apprehended by Profs. 

 Schultze and Williamson ; the former of whom (xcvii) has reunited the genera Trilocidina 

 and (luinqudocuHna under the generic designation Miliola ; whilst the latter (ex) has brought 

 them together under the name Miliolina, with the addition of Adelosina, which he rightly 

 states (p. 89) to be nothing else than a young form of the same type, distinguished by the 

 peculiar retort-shape of the primordial and the next succeeding chambers. Prof. Williamson 

 truly remarks (p. 80) that "none of the Foraminifera are more liable to variation than those 

 comprehended in the Lamarckian genus Miliolitcs ;" and adds (p. 87), that some of his "most 

 able correspondents, who previously thought that the species of Miliolinm ought to be made 

 much more numerous, on endeavouring to group the specimens in their cabinets according 

 to such views, found their difliculties increase with the multiplication of their specimens." 



103. External Characters and Internal Structure. — The essential plan of conformation in the 



