82 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



umbilical angle on the inferior surface of the last chamber, more or less protected by a 

 valvular tongue. 



The structure and affinities of the genus Valvulina have been very completely 

 worked out by my friends Messrs. Parker and Jones, and to their general results, 

 as stated by Dr. Carpenter (" Introduction," p. 146), I have little to add. But hitherto 

 no specimens proper to the genus have been recorded as such from any formation older 

 than the Chalk, and the discovery of a number of new forms pertaining to a much 

 earlier geological period brings with it considerable accession to our knowledge of the 

 modifications which the type assumes. 



British rhizopodists have generelly accepted d'Orbigny's model of Valvulina 

 triangularis (Modele No. 25) as the best central type of the genus. This is a trifacial 

 and triserial pyramid, somewhat rounded at the thick end and showing the characteristic 

 aperture. Variations from the typical form run in two opposite lines either the axis 

 of the spire becomes shorter, giving rise to the trochoid and outspread varieties, in 

 which the salient characters are only recognised in a sub-arenaceous texture, valvular 

 aperture, or tendency to triserial arrangement of chambers, as in Valvulina Austriaca 

 ('For. Fos. Vien.,' p. 181, pi. 11, figs. 7, 8 l ) , or on the other hand, the spiral portion, 

 retaining its original form, is supplemented by the growth of a line of chambers from 

 its broad end, forming a cylindrical, uniserial column, with a pointed, triangular, triserial 

 base, as in Valvulina (Clavulina) Parisiensis (Modele No. 66). The latter modifica- 

 tion finds its extreme expression in Valvulina davulus (Modele No. 2), in which the 

 spiral end is entirely lost, and a rectilinear series of arenaceous segments with valvular 

 mouth alone remains. 



Wide as is the range of characters embraced in the above description, considerable 

 latitude must still be allowed in its application to individuals or even to sets of 

 specimens. I have long been convinced, from observations on recent specimens, 

 especially from a series collected on the west coast of Scotland, that even the triserial 

 habit of growth is not a character to be relied on, and it has been no matter of surprise 

 to me to find that in the Carboniferous Limestone beds there exists a set of forms, more 

 closely allied to Valvulina than to any other recognised genus, in which the number of 

 chambers in each convolution is altogether variable, and of no significance as a generic 

 peculiarity. Indeed, in the species about to be described, four is on the whole a more 

 common serial number than three a fact that seems to have been noticed by Ehrenberg 

 and to have suggested the name Tetrataxis for the genus which he founded to embrace 

 some of the varieties. 



As to the position of the genus Valvulina, little need be added to what appears in 

 Dr. Carpenter's work (loc. cit.). It is there referred to the sub-order " Imperforata " 



1 Tliis is the Rotalina fusca of Williamson, ' Rec. For. Gt. Br.,' p. 55, figs. IN, 115. 



