4 STR0BILOPSID.5:. 



our conceptions of this intricate group, though it is admitted 

 that they are not strongly characterized families. 



Paleontology. 



Strobilopsidae appeared in the Upper Eocene of western 

 Europe in several species having all the external characters 

 of the genus Sirohilops, and though the internal structure has 

 not been worked out, it is safe to assume that they are closely 

 related to the well-known Oligocene forms following them. 

 In Europe this genus continued in numerous species into the 

 Pliocene, the last one in the Upper Pliocene (Astian stage) 

 of Piedmont. 



In late Cretaceous beds there are various forms described 

 as Helix, or under the names 01)'biniila and PseudostroMlus, 

 which certainly have some of the characters of Strohilops. 

 The poor preservation of the very small number of specimens 

 yet found does not admit of a definite reference to this family ; 

 their position can only be cleared up by further material. 

 All are larger than any Strohilops. Notes and references, with 

 figures of the type species of these groups, follow the list of 

 Tertiary species of Strohilops. 



Genus Strobilops Pilsbry, 



The following list is taken from that of W. Wenz, Fossilium 

 Catalogus, Pt. 20, III, 1923, pp. 1041-1061, which must be 

 consulted for full references to previous literature. A few 

 minor alterations and additions have been derived from other 

 sources. 



Strohilops appeared in the upper Eocene in three species. 

 Oligocene species are more numerous and their structure has 

 been fully investigated. Some, such as S. headonensis and 

 S. pseudolahyrinthica, carefully worked out by L. R. Cox, 

 approximate rather closely to recent species of the typical 

 labyrinthica group, having the interparietal lamella developed, 

 the series of internal plicae extending above the periphery, and 

 the exterior costate. This group continued into the Pliocene, 

 represented by several species, S. romani (pi. 12, figs. 11-13), 

 S. lahyrinthicula and others. 



