84 CARBONIFEROUS AND PERMIAN FORAMINIFERA. 



Characters. Test free or adherent, spiral, trochoid ; composed of several convolutions, 

 each of which consists of from three to four thin, oblique segments, all more or less 

 visible on the exterior. Chambers simple, not sub-divided into chamberlets. Septation 

 externally obscure, sometimes marked by slightly depressed or excavated lines. On the 

 inferior surface the outline of the three or four chambers of the last convolution may 

 sometimes, though rarely, be traced, each chamber with a projecting lip directed over a 

 sort of umbilical vestibule. Diameter, -^ inch (0'86 mm.). 



So far as the British Carboniferous beds are concerned, Valvulina pal&otrochus is one 

 of the most striking and best differentiated species of Foraminifera. In shape and habit 

 it bears some external resemblance to the recent Valvulina conica, but its shell-texture is 

 less coarse and heterogeneous, owing to the constituent particles being entirely or almost 

 entirely calcareous, whilst in the living species the test is commonly built up of siliceous 

 sand and ferruginous cement. There is quite sufficient evidence that, like the analogous 

 recent form, V. palaotroclms is normally parasitic, though the fossil specimens are seldom 

 found actually in that condition. This is probably due in part to the unevenness of the 

 base of the shell preventing very close adhesion to foreign bodies, or perhaps to the muddy 

 condition of the sea-bottom offering but few facilities for adherent growth. Professor 

 Ehrenberg gives two sets of figures under different names on the plate above quoted, but 

 there can be no doubt that they refer to the same species ; those in Section X from the 

 Bellerophon-limestone of Witegra, on Lake Onega, Russia, have apparently been 

 obtained free from the matrix, whilst the drawings in Section XI of the same plate, of 

 specimens from the Mountain Limestone 1 of Tula, Russia, represent transverse and 

 perpendicular sections viewed by transmitted light. 



Well-defined examples of Valvulina palceotrochus cannot be confounded with those 

 of any other Carboniferous species, except it be V. Younffi. In external contour these 

 two forms are exceedingly similar, but the characteristic sub-division of the seg- 

 ments of the latter into numerous chamberlets is generally indicated with more or less 

 distinctness by superficial markings, and when this is not the case, a broken specimen, 

 or still better a transparent section of the shell in a perpendicular direction, affords a 

 ready means of diagnosis. Valvulina palteotrochus differs from V. decurrens and 

 V.plicata in relative height and diameter, and in the mode of septation. Good specimens 

 have a height nearly equal to the diameter of the shell at the base, and the spiral course 

 of the chambers is much obscured by the extreme obliquity of the septation. On the 

 other hand, V. plicata has but little more than half the relative height, the margin is 

 rounded, and the septation almost Rotalian ; whilst V. decurrens is still thinner, 

 sometimes a mere scale, and its spiral growth is frequently rendered conspicuous by the 

 partial or entire obliteration of septal lines and the consequent apparent absence of seg- 

 mentation, as shown in PI. Ill, fig. 18. 



1 Described as " Hornstone of the Mountain Limestone with Spirifer mosquensis." 



