298 BALAN1M1. 



valve ; placed at about its own width from the basi-scutal angle ; basal 

 end bluntly pointed ; the basal margin on the opposite sides of the 

 spur forms a nearly straight line ; the carinal margin has an extremely 

 narrow border formed by upturned lines of growth. Internally, the 

 surface is roughened with little points : the articular ridge is prominent : 

 the crests for the tergal depressores moderately prominent. 



Parietes : the longitudinal ribs on the internal surface are either 

 feebly, or, in the lower part, strongly developed ; their basal ends are 

 only just perceptibly denticulated. As already stated, in about half 

 the specimens, there were no traces of parietal pores ; in the other 

 half there were either distinct or obscure pores ; the pores are circular, 

 generally of unequal sizes, and never large ; in the same individual 

 they would sometimes be almost wholly absent in some of the compart- 

 ments, and quite plain in the other compartments. The Radii are 

 either moderately wide or rather narrow, and have their upper margins 

 very oblique, and not distinctly arched, and not quite smooth : their 

 sutural edges are very finely crenated, the teeth or septa not being 

 denticulated. The upper margins of the alee are rather less oblique 

 than those of the radii : their sutural edges are barely crenated. The 

 basis is thin, and without any trace of pores ; the upper surface is some- 

 times furrowed in radiating lines. 



44. Balantjs varians. PI. 8, fig. 9. 



B. varians. G. B. Sowerby, in Darwin's Geolog. Observ. on South 

 America, (Sept. 1846), Tab. 2, fig. 4, 5. 6. 



Parietes moderately thick : radii with their upper margins 

 very oblique ; sutural edges almost smooth, or finely crenated : 

 basis finely porose. Tergum tvith the spur small, narrozv, 

 bluntly pointed. 



Hah. — Port St. Julians, Patagonia; ancient Tertiary formation. Eastern 

 plain of Tierra del Puego (?) 



This species comes so close to B. unguiformis, that I have 

 some doubt whether they ought to be specifically separated : 

 the whole shell is stronger, and the basis can be seen to be 

 porose when a polished section is made : the spur of the 

 tergum is smaller, more pointed and more medial, but 

 these latter differences may be due to mere variation. Should 

 B. varians and ungiuformis prove to be the same species, 

 the latter name has the priority. 



General Appearance. — Shell moderately strong and thick ; shape 

 conical or tubular, or even inverted conical ; orifice moderately 



