BIGENERINA. TRUNCATULINA. 137 



Textularia of the stout thick-shelled type, like T. gibbosa, with the addition of a line of 

 two or three inflated subcylindrical segments. The tendency to the labyrinthic interior 

 structure, which characterises the larger Texfularite, is strikingly seen in such specimens 

 as PL X, figs. 30 and 31, and so far as it goes confirms the relationship. M. d'Orbigny 

 in his generic description lays some stress on the regular and equilateral contour of the 

 shell ; hut occasional slight asymmetry, as exhibited in fig. 30, cannot be regarded as of 

 any morphological importance. 



Distribution. In England Bigenerina patula has only been found in the Saccam- 

 mina-limestone of Elfhills, Northumberland ; in Scotland it is equally rare, having 

 been noticed in but one locality, belonging to the Lower Carboniferous Limestone Group. 

 Specimens are occasionally, though rarely, met with in the friable Fusulina- limestones of 

 Russia. 



Genus. TRUNCATULINA, d' Orbigny. 



TEST/E HAMMONIFORMES (in part), Soldani. 



NAUTILUS, Walker and Jacob, Gmelin, Fichtel and von Moll, Maton and Rackett, Pennant, 



Dillwyn, Turion. 

 SERPULA, Montagu. 

 POLYXEXES, CIBICIDES, de Montfort. 

 LOBATULA, Fleming, Thorpe. 

 TKUXCATULIXA, d'Orbigny, Roemer, von Hag enow, Reuss, Parker and Jones, Williamson, Seguenza, 



Carpenter, Dauison, Brady, Gilmbel, Sars, Robertson, Parfitt, Fanden Broeck, fyc. 

 ROSAIINA (in part), Alth, Reuss. 

 BOTALINA (in part), Reiiss. 

 PLANORBULINA, Parker and Jones, Carpenter. 



General characters. Test parasitic, spiral ; outermost convolution alone visible on 

 the inferior 1 lateral surface ; all the convolutions, including the ultimate segment, appa- 

 rent on the truncate, superior (adherent) surface. Segments numerous ; convex below, 

 flat, and truncate above. Orifice single, in front of the ultimate segment, close to the 

 carina of the preceding convolution and continued, as a fissure, along the superior con- 

 necting spiral, at the expense of the umbilical borders of the last two or three segments, 

 but closed in by superimposed layers of shell in all the remaining ones. 



It would be more strictly correct to speak of Truncatulina as a subgenus of 



1 D'Orbigny in his various descriptions speaks of the spiral surface of the test of the Truncatulina as 

 the " lower " surface because it happens to be flat, and vice vend. Williamson and others, having regard 

 to homology, treat the spiral surface in all the Rotaline genera as the " superior " surface. The anomaly 

 in Truncatulina is apparent rather than real, whilst uniformity in terminology is a matter of solid 

 importance. 



18 



