210 



THE GEOLOGIST. 



columella. In one gernis, however, Chilina (Gray), tlie conditions 

 of the spire and the aperture are much modified ; the columella is 

 curved, but is without the oblique twist of the true Limnoea, which is 

 replaced by one or more transverse folds. One species in this group, 

 C. PeJmelcha (D'Orb.), closely resembles the fossil in question, in the 

 relative proportions of the spire and the aperture, and the general form 

 and aspect of the shell. In another species, G. Puelcha (D'Orb.), 

 the transverse fold is almost obsolete in the young state, and is much 

 reduced in importance in the mature shell, while the curve of the 

 columella and the rounded front of the shell correspond with those 

 of the Peckham fossil. The Ghilinoe are described by D'Orbigny as 

 inhabitants of the clear running streams and rivers of Chili and 

 Patagonia, habitats to which the occurrence of Glandina costellata 

 and of Helix lahyrinthica as Eocene fossils, would prepare us, in some 

 measure, to look for a living analogue of the form in question. 



Externally the columella of the fossil shells appears, to be straight 

 and simple, but in specimens, in which the inner surface is more dis- 

 played, there are indications of a slight and very oblique twist ; and 

 I am induced, therefore, on the whole, to consider these shells as 

 constituting an aberrant form among the Lhnnw idee, partaking of 

 the characters of the true I/lmncea and of Ghilina, and to place them 

 between those genera under the generic name Pitliarella ; and I dedicate 

 the species to Mr. Hickman, by whom attention was first drawn to 

 these interesting shells. I subjoin a description of the principal cha- 

 racters which distinguish the genus, and also a description of the 

 species. 



Hanipstead, 6t]i May, 1860. 



Pitliarella (Gen. char.). — Shell sub- cylindrical ; spii'e obtuse, more 

 or less produced ; apertm*e oval-oblong, rounded in front, narrowed 

 behind ; columella straight, or very obliquely twisted, arched ante- 

 riorly ; outer lip simple, acute ; inner lip thickened. 



P. Bichnani (Spec, descr.). — Shell oval-oblong, smooth; spire sub- 

 conical, short, varying in height in difierent specimens ; whorls five 

 or six, depressed on the posterior margins, and obtusely angulated 

 on the shoulders. The sutui'al edge is slightly thickened, forming 



