MARYLAND GKOLOGICAL SURVEY 465 



septal lilies beiug more curved on the superior surface; aperture a small 

 neatly shaped arch at the inferior mai-gin of the ultimate segment. 



Those characters are subject to considerable variation and when the 

 forms become highly convex the species grade over into the Truncatulina 

 refalgcns type, while those forms more flattened constitute Truncatulina 

 wuellerstorfl. Those regularly and symmetrically developed constitute 

 Truncatulina houeana d'Oi*bigny and the less regular form the Trunca- 

 tulina variabilis of the same author. Both of these forms T. lohatula 

 and T. variabilis are abundant in the Atlantic coast Miocene deposits. 



As a fossil it is one of the most abundant tyi)cs and is very widely dis- 

 tributed over existing oceans. It is also of great range bathymetrically 

 speaking, occurring at all depths down to 3000 fathoms. 



Its geological appearance dates from the Carboniferous period. 



Occurrence.— CiiovTA'KK Formation. Jones Wharf, Pawpaw i'oiut, 

 Governor Eun, Peach Blossom Creek. Calvert Formation. Plum 

 Point. 



Collection. — Maryland Geological Survey. 



Truncatulina variabilis d'Orbigny. 

 Plate CXXXI, Figs. 9, 10. 



'fruni-iitiilitKi. /'itridhiliti d'Orbigny, 1820, Ann. 8ei. Nut., vol. vii, \>. '.i7'.), No. 8. 

 Truncatidiiui vnrlntiUiH Tercincun, 1878, M('ni. Soc;. (i(M)l. KruMcc, scr. !5, vol. ii, 



Mem. ill, p. 1, ligs. 18-25. 

 TruncutidiiKi I'nridhUis Bag{(, 18',t8, Hull. Ainur. I'al., No. 10, [>. '■'>(>, \>\. ii, lig. 5. 



Description. — Test consisting of a depressed, plano-convex, exceedingly 

 variable form, the segments of which are never uniform or regular in 

 arrangement as in Truncatulina lobaiula but are more or less evolute and 

 vary also in the amount of compression and form. The shell is coarsely 

 perforate. The aperture is a wide gaping arch extending along the 

 inner margin of the final convolution. 



This species is very abundant in the Miocene deposits of Maryland and 

 Virginia. Its first recorded appearance as a fossil is from the Eocene 

 of the Paris basin though it is probably of much earlier occurrence. 



Occurrence. — Ciioptank Formation. Jones Wharf, Pawpaw Point, 



Governor Eun, Peach Blossom Creek. Calvert Formation. Plum 



Point. 



Collection. — Maryland Geological Survey. 

 30 



