68 Transactions of the Boijal Microscopcal Society. 



The now nearly extinct Dactyloporidse are far less evidently 

 allied to the other Forcellana above mentioned, than the latter 

 are amongst themselves. Their simplest form of shell (Eajjlo- 

 •oorella), however, consists of little sacs, or bottle-shaped chambers, 

 repeated in lateral apposition; and in more complex forms there 

 is a structure approaching that in old Orhitolites. 



In these points, besides the similarity of shell-tissue, the several 

 groups of the Porcellana approach one another ; but the Dactylo- 

 'poridm seem to stand somewhat apart, wanting links, hidden, per- 

 haps lost, in the older rocks. The high-class " hyaline " Thalamo- 

 ^ora reminds us of some features in the structure of Dactijlopora. 



Shells of the Arenacea. — The Foraminifera arenacea divide 

 themselves at first sight into three sets: — 1. Those which always 

 have a sandy shell {Lituola, Trochammina, &c.) ; 2. Those which 

 have a partly perforate and partly sandy shell ( Valvulina) ; and 3. 

 Those which are clear in the young and sandy in the old stages, as 

 Textularia and Bulimina, and sometimes SpirolocuUna, Quinque- 

 loculina, and Ntibecularia. 



The persistently arenaceous forms are also divisible into two 

 kinds : — 1. Those with fine-grained sand in the shell-cement, and 

 mostly smooth {TrocJiammina, &c.) ; and 2. Those with coarser 

 grains, less cement, and a rough surface [Lituola, &c,). In some 

 cases sponge-spicules are partly or wholly used in the construction 

 of these tests. There is great difficulty, however, among the innu- 

 merable modifications of the arenaceous Foraminifers, in drawing a 

 line between relative roughness and smoothness of shell, abundance 

 and scarcity of cement, and coarseness and fineness of materials ; 

 and we are led from the rongh lituate, to the smoother nautiloid 

 Lituoloe, and on to the rotalioid Trochamminm, and thence to 

 Valvulina, until the whole series becomes apparently indivisible.* 



Of the rough-cast sand- shells, with a minimum of cement, 

 Lituola is the leading type. It takes the well-known lituate shape ; 

 but frequently also it imitates Lagena, Nodosaria, Orthocerina, 

 MarginuUna, FlahelUna, Bulimina (?), Nonio7iina,Sind Glohigerina 

 so closely that, excepting for its internal labyrinthic structure and 

 cribrate septa, the sandy coat would seem to belong as rightfully 

 to these as a hyaline shell. My friend, Mr. H. B. Brady, F.K.S., 

 tells me, indeed, that it is very difficult to say whether or no the 

 earliest (palaeozoic) Nodosarias had normally clear, or opaque, or 

 sandy shells. 



In his description of Quinqueloculina fusca,] Mr. H. B. Brady, 

 F.K.S., points out that it differs from Q. agglutinans % in having a 

 tough, flexible test with a very little amount of calcareous or earthy 



* Brady, ' Aniuils Nat. Hist.,' ser. 4, vol. x., p. 2G1. 

 t ' Aimals Nat. HLt.,' ser. 4, vol. vi., pp. 27G, 286. 

 X Op. cit., p. 48. 



