208 PROCEEDINGS OF THE ACADEMY OF [May, 



a contribution to the morphology of pyrula. 



by burnett smith. 



Introduction. 



At the pi'csent day the genus Pyrula^ is made up of a small number of 

 species and these, though differing from one another somewhat, are 

 nevertheless all very much alike. The thin shell, cancellated sculpture, 

 low spire and long anterior siphon are common to them all. There is 

 no exaggeration in saying that nowhere among the marine gastropods 

 do we find a set of species which are with better reason arranged in one 

 generic group. They are indeed distinctly monophyletic. On examin- 

 ing the fossil Pj'rulas we find that the genus gives us a homogeneous 

 series of species ranging back in time well into the Eocene. It is true 

 that Pyrula is seldom a common fossil in any formation, and likewise 

 it does not furnish us with great series of closely related races which 

 follow^ one another in the rocks of any continuous geological section. 

 Nevertheless the very homogeneity of the scattered fossil species comes 

 to our aid. Their distinctly peculiar shell characters are always present, 

 just as in the widely distributed living forms. 



The. desire to deal with a group w^hose monophyletic nature is above 

 suspicion has led the author to exclude from the present paper many 

 Eocene and earlier species which are usually assigned to the genus. 

 Not a few of these may be indeed very close to Pyrula, but the present 

 paper has for its object the recording of the changes which a mono- 

 phyletic assemblage of species actually exhibits when w^e trace its 

 members through the different episodes of the time range and from one 

 geographical province to another. Still other early species appear to 

 be referable to Pyrula, but the preservation of the specimens is not good, 

 and this is an essential for a proper understanding of the shell sculpture 

 and apical characters. These forms also must be omitted. 



^ This paper is intended merely as a study of some of the morphologic changes 

 in a monophyletic group and makes no pretense of being a systematic re\'ision 

 oi the genus. Most of the specific tj^pes are either undesignated, lost or vmavail- 

 able, and the author has learned by experience that the average published figure 

 of a species of Pyrula is extremely unreliable. For these reasons the propriety 

 of using the generic name Pyrula is not here considered, and the classification in 

 Tryon's Manual of Conchology has been followed in discussing the recent forms. 

 In dealing with the fossil species references are given in each case. 



