722 
DE. W. B. CARPENTER AND ME. H. B. BEADY ON 
and T. Rupert Jones, they were led to recognize it as having the same fundamental 
value in a systematic point of view as the Vitreous and Porcellanous types ; and it was 
in accordance with their representations, that, in my “ Introduction to the Study of 
the Foraminifera ” (1862), this type was recognized as characterizing a third great 
Primary Division of the group. It was pointed out, however, that “ to separate all the 
Foraminifera that form Arenaceous shells from those of the Porcellanous and Hyaline 
types, to which many of them obviously bear the closest affinity, would be a violation 
of the first principles of a natural arrangement ; and yet we shall find that there are 
certain generic types in which the sandy texture is a character of great systematic 
importance.” In certain genera, alike of the Porcellanous and of the Vitreous series, 
the surface of the true shell is often covered with an arenaceous incrustation ; but this 
is a character that does not justify even specific differentiation. It is only when the 
whole thickness of the 4 test ’ is composed of agglutinated sand-grains, and when “ certain 
assemblages of forms, constituting well-marked generic types, can be uniformly charac- 
terized by the possession of Arenaceous shells, — as is the case with Trochammina, 
Lituola, and Valvulina ,” — that we are enabled to recognize the distinctive value of this 
peculiarity, as marking “ a fixed and decided physiological character, the occurrence of 
which elsewhere is only occasional or incomplete.” It was further pointed out that the 
absence of pseudopodial pores in the shells of this group shows their affinity to be 
rather with the Porcellanous than "with the Vitreous series, notwithstanding the very 
close resemblance which some of them present to particular types of the latter (op. cit., 
pp. 46-48). 
At the time that the Chapter “ On the Principles of Classification ” in the Treatise 
just cited was passing through the press, I learned with great satisfaction that Professor 
Reuss of Vienna, — the highest Continental authority upon this group, — had fully 
accepted the doctrine laid down in my previous Memoirs, that the composition and 
intimate structure of the Shell are characters of primary importance in Classification, 
and that little value in comparison is to be attached to Plan of Growth ; and that he 
had communicated to the Imperial Academy of Vienna a Systematic Arrangement based 
on these principles, essentially corresponding with that which I had myself worked out 
with the assistance of my able coadjutors (Messrs. W. K. Parker and T. Rupert Jones), 
— except in the retention of the distinction between the Monothalamia and the Poly- 
thalamia, of the validity of which, however, he expressed himself doubtful*'. In this 
scheme, as in our own, the essentially Arenaceous types were ranked together in a 
distinct group, which, like ourselves, he regarded as allied (in virtue of the absence of 
pores) rather to the Porcellanous than to the Vitreous series. And having subsequently 
come to the conclusion (which I had explicitly stated in the Chapter just referred to, 
§ 52) that the distinction between the Monothalamia and the Polythalamia cannot be 
maintained, he so modified his scheme in a “ Nachschrift,” that it came to present a most 
* Sitzungsberichte der Hathem.-naturw. Classe der Kaissrl. Akad. der Wissenschaften ; Bd. xliv., Wien, 
1861, S. 355-396. 
