Vol. XVII. PP. 1-16 February 5, 1904 



t 



PROCEEDINGS 



Otr THK 



BIOLOGICAL SOCIETY OF WASHINGTON 



^^ '"; 



AS 



SYNOPSIS OF THE GENERA, SUBGENERA AND SEC- 

 TIONS OF THE FAMILY PYRAMIDELLID^. 



BY WILLIAM HEALEY DALL AND PAUL BARTSCH. 



The Pyramidelliclse, a family of Mollusks mostly of small 

 size and world-wide distribution, occur fossil first in the Creta- 

 ceous, are numerous in the Tertiary, but perhaps are most fully 

 developed in the existing faunas. Very numerous names have 

 been applied to them, sometimes under the impression that the 

 pillar is not plicated in a particular group, a mistake which, by 

 grinding down the whorls, can be corrected; the missing plica- 

 tions being present but falling a little short of reaching a point 

 in the aperture where they are visible externally. In all the 

 forms of which the soft parts are known the external anatomy 

 is very similar. In examining a large series of forms, as noted 

 by Fischer.^ intermediate types appear until it becomes a matter of 

 great difficulty to decide where, if anywhere, the generic lines 

 can be drawn, and it is not surprising that some authors have 

 fallen back on the expedient of regarding most of the species, 

 notwithstanding the contrasting extremes, as belonging to a 

 single genus. Where a group is composed of such a multitude 

 of species it seems more convenient in practice and leads more 

 efficiently to clear thinking, to take the other view, and subdi- 



1— PROC. BIOL. SOC. WASH. VOL. XVII, 1904. (1) 



