﻿NODOSINELLA. 



103 



material. Such, in general terms, are the relations of Nodosinella ; the details may best 

 be gathered from the specific descriptions. 



In observations on the structure of the tests of Foraminifera it is needful to bear in 

 mind the conditions under which the animals have lived. A creature of low organization 

 and limited selective power, building its investment chiefly of extraneous materials, 

 and secreting only the cement by which such materials are incorporated, forms a test which 

 must necessarily vary with the nature of the sea-bottom on which it lives. During the 

 Carboniferous Limestone period the sea-bottom was for the most part a fine calcareous 

 mud, seldom containing any appreciable quantity of siliceous material in the form of sand, 

 so that the composite tests of minute organisms must of necessity have been chiefly 

 made up of calcareous particles incorporated by calcareous cement, and as a natural 

 result the texture, which under other conditions would have been heterogeneous and 

 granular, is compact and nearly homogeneous. 



But notwithstanding the smooth exterior which these, in common with other Car- 

 boniferous subarenaceous forms, often possess, there is seldom much difficulty in proving 

 their composite structure, and the absence of any trace of shell-perforation is a con- 

 firmatory fact of some importance. Although the tendency of calcareous infiltration is to 

 obliterate minute markings, specimens would surely have been found, to judge by the 

 Nodosarice of the Permian Magnesian Limestones, affording some evidence of shell- 

 perforation if it existed; but, notwithstanding rigid examination, nothing of the sort has 

 been detected in any of the species which have been assigned to this group. That these 

 smooth subarenaceous Carboniferous forms were the precursors of the true Nodosarice 

 of the Permian is an interesting and significant fact, whatever may be their zoological 

 relationship. 



Nodosinella digitata, nov. PI. VII, figs. 1 — 3. 



Characters. — Test elongate, tapering ; straight or only slightly curved ; cylindrical or 

 somewhat compressed. Segments irregular, more or less inflated. Aperture single, 

 simple. Length to ^2 mcn (1*0 to 2'0 mm.). 



The coarse imperforate test alone distinguishes this form from the Nodosaria, for the 

 septation, though often partial and obscure, is sometimes at least as well defined as in 

 Nod. {Dentalind) pauper ata, and other similar varieties of the hyaline type. Figures 1, 

 2, and 3 of Plate VII are all from Permian specimens : — fig. 2 is a neatly septate, somewhat 

 flattened variety, but connected by gradational links with the stouter, rounded type ; 

 whilst fig. 3, by its indistinct septation, approaches in character the group of Carboniferous 

 forms which immediately follow it in the plate. As has been repeatedly stated, it is 



