92 FORAMINIFERA OF THE CRAG. 



other Foraminifera, has been further illustrated by MM. Munier-Ohalmas and 

 Schlumberger, whether it be formed by the outside of the chamber last invested 

 or by a subsidiary shell-growth. 



As the recognition of the separate species and varieties is, for general purposes, 

 based on the external features of the test, and these are liable to a wide range 

 of variability in individual growths, there is little need of altering the names as 

 given in Part I of this Monograph, except with regard to Triloadina and Quinque- 

 locuUna (pp. 7 — 14), the necessity for which change the synonymy of Miliolina 

 ohlonga (pp. 7 and 8) sufficiently supports in the direction of the views above 

 refei'red to. 



The special biological value of the presence of either a large (A) or a small 

 (B) initial chamber in any Foraminifer has been a chief subject of study by Dela 

 Harpe and other observers above mentioned, but definite results have not yet been 

 arrived at. 



Those Nummulites grouped under A are generally " free-growing individuals, 

 soon arriving at their limit of growth " (P. and J., 1861) ; whereas the others (B) 

 attain a larger relative size. This variation in the individuals of one species M. 

 Munier-Chalmas at first (1880) termed " dimorphism," with a different application 

 from that of Dimorphina (d'Orbiguy, 1846), and " dimorphous " (P. and J., 1860), 

 and " trimorphism " (P. and J., 1863), which have reference to successive stages 

 from one style of growth to another. The later expositions, however, by Munier- 

 Chalmas and his colleague of the growth of the MilioUdas (as noticed above) may 

 be said to give the term its full meaning as to the passage-forms in individuals 

 altering their plan of growth, without reference to the primordial chamber. As 

 the dimorphous forms of Miliolina, Peneroplis, Lituola, Textilaria, ValviiUna, 

 Polymorphina, and some of the Nodosarinae, &c., though severally grouped under 

 *' generic " names,^ are plainly referable to their zoological type-forms, so the 

 Miliolidse and allied groups still hold their suzerainty over the more or less differ- 

 entiated forms, whether species, sub-species, or varieties, elucidated of late by the 

 careful diagnoses elaborated by our esteemed fellow-workers in France (see a 

 note on " Dimorphism " in the ' Annals and Mag. Nat. Hist. Soc.,' Ser. 6, vol. xiv, 

 1894, pages 401—407). 



There is, of course, great difficulty in deciding the relative value of differences 

 among individuals (of all the groups) showing modifications (often inconsiderable) 

 or deviations from the zoological type, whether due to idiosyncrasy of the individual 

 or to evolution among the many, for they may have been caused by accidents of 



* Such as Articulina, Spirolina, HaplopJiragmium, Bigenerina, Spirophcia, Qaudryma, Clavu- 

 lina, Amphicoryne, Flabellina, Marginulina, Dimorphina, Sagrina, &c. 



