72 Transactions of the Royal Microscojncal Soeietij. 



value as indications of peculiar conditions of habitat ; and because, many of them 

 IH-esenting at first sight striking ditferences of form, size, and ornamentation, 

 and being easily mistaken for types of distinct specific groups, they have acquired 

 an importance in the eyes of zoologist and geologist which makes it convenient to 

 give them a sort of subspecific value and a binomial term. 



" It has been doubted by some whether in this, the most variable, because 

 simplest, family of the animal kingdom, every variety should not be distinguished 

 by its own binomial appellation, — a plan that has been followed almost to the 

 full by many naturalists. In this, however, we cannot agree, for the unlimited 

 multiplication of quasi-specific names, linked together by pseudo-generic titles, 

 can only weary the catalogue-maker, and throw obstacles in the way of the syste- 

 matist ; for it keeps up a false notion of the value of external characters which are 

 rarely essential, whilst no clue is thereby obtained to the morphological law of 

 each real specific type. Evidences of such law, however, are not wanting when 

 •we carefully examine varietal forms as they diverge, and, as it were, radiate, from 

 a given central type. 



" Though Linna3us was somewhat parsimonious in giving names to the micro- 

 scopic shells which he knew, and though Fichtel and Moll partially indicated 

 their great variability, and were cautious in naming tiiem, yet it was not until 

 Dujardin demonstrated the nature of the Rhizopodous sarcode and its simple, 

 non-diflerentiated character, and until Williamson r.nd Carpenter, taking up the 

 study of certain species, showed wliat extreme forms might be connected together 

 by innumerable gentle intermediate gradations, that anything like a really 

 scientific appreciation of these Microzoa may be said to have existed. Our own 

 experience of the wide limits within which any specific group of the Foraminifera 

 multiply their varietal forms, related by some peculiar conditions of growth and 

 ornamentation, has led us to concur fully with those who regard nearly every 

 species of Foraminifera as capable of adapting itself, with endless modifications 

 of form and structure, to very different habitats in brackish and in salt water, — 

 in the several zones of shallow, deep, and abyssal seas, — and under every climate, 

 from the poles to the Equator. Our principles of nomenclature, and the applica- 

 tion of them, may be seen in our papers on Foraminifera in the ' Annals and Mag. 

 Nat. Hist." " 



Hyaline or Perforate Foraminifera. — The typical shell of a 

 " hyaline " or " perforate " Foraminifer is, iu its simplest form, a 

 very thin, calcareous, perforated tissue, as in an Orhdina, or in 

 a young Glohiyerina, or in the primary segments of a Nummulina. 

 In the Lagenida this early shell is more compact than in some 

 other groups, but still minutely perforate. With the growth of 

 additional segments (whether in straight, curved, or alternate 

 arrangement), the chambers become coated, by the investing sar- 

 code, with successive layers of shell; and the primary layer, 

 whether soft and friable, or relatively hard and glassy, becomes 

 thickened ; its perforations, however, are usually kept continuous 

 with the tubules in the succeeding layers by the presence of the 

 pseudopodia, between and around which the little prism-like consti- 

 tuents of the simple shell are formed. According to the number 

 of successional layers, the chamberwalls necessarily vary in thick- 

 ness, either uniformly or with inequalities. 



These latter originate variously; for instance, 1. From the 

 superabundant shellmatter laid down on spots or Hues, as pimples 

 and prickles, or as thick and thin ridges, as in the Lagenida. 

 2. Thickenings over certain structures, as over the edges of septa, 



